Labor Unions and Voter Turnout in the American States: Direct Versus Indirect Mobilization

Abstract

I examine the relationship between labor unions and voter turnout in the American states. Though it is well known that unions increase turnout directly, we know less about their indirect effects. Moreover, the indirect effects may consist of nonmember mobilization and aggregate strength. To examine the direct and indirect mechanisms, I analyze both state-level panel data and individual-level data with a multilevel approach. First, my panel analysis shows that unions are positively associated with turnout as expected. Yet, the association is observed only in midterm elections, but not in presidential elections. Second, more importantly, my individual-level analysis suggests that indirect nonmember mobilization and indirect aggregate strength are positively related to turnout, while direct member mobilization is not. The findings imply that the direct effects are limited and, thus, that decreasing levels of voter turnout due to recently declining union membership come primarily from indirect mobilization rather than direct mobilization.

Introduction

Scholars have suggested that organizations play a key role in shaping political attitudes of their members because they are “the backbone of civil society—lying between the personal world of the family and the public world of politics” (Verba, Schlozman, and Brady 1995, 369). Labor unions, as one of membership organizations, also have been considered a channel of political socialization to affect political attitudes of their members. Previous studies have found that because workplace is a context for political interactions (Hertel-Fernandez 2018; Mutz and Mondak 2006), labor unions shape racial attitudes (Frymer and Grumbach 2021), and policy attitudes such as welfare state (Hasenfel and Rafferty 1989) and trade (Ahlquist, Clayton, and Levi 2014; Kim and Margarlit 2017) among others (Ahlquist and Levi 2013; Francia and Bigelow 2010). In addition to the role of labor unions in shaping political views, their mobilizing impact on voter turnout also has been found in American politics (Ahlquist 2017; Lamare 2010; Leighley and Nagler 2007; Radcliff 2001; Rosenfeld 2014) as well as in comparative contexts (Flavin and Radcliff 2011; Gray and Caul 2000; Radcliff and Davis 2000).

However, prior studies analyzing the relationship between labor unions and turnout have been interested primarily in direct mechanisms. Thus, we know less about their indirect mechanisms. Specifically, some scholars clearly demonstrate that union membership is positively related to voter turnout at the individual-level (Leighley 1996; Leighley and Nagler 2007; Rosenfeld 2014), while others also provide empirical evidence that aggregate state union density is positively associated with higher voter turnout at the state-level (Leighley and Nagler 2007; Radcliff 2001; Radcliff and Davis 2000). Yet, even though still others consider the impact of individual nonmember mobilization, they suffer from analytical shortcomings, which I discuss in detail below (Leighley and Nagler 2007; Radcliff 2001). Moreover, it is well known that membership rates of labor unions—especially, private-sector union membership—keep decreasing in recent decades (Rosenfeld 2014). The OECD data shows that labor union members account for about 11% of workers (about 15 million workers)—but, less than 10% of private-sector workers—in the US. Given the decline of union membership, the question of whom and how labor unions mobilize has become more important because it might not be enough for union leaders to mobilize only their members via direct mobilization. In this paper, I therefore estimate the direct and indirect mechanism of labor unions with regard to voter turnout using newly updated data.

To do this, I analyze both state-level panel data and individual-level data with a multilevel approach. First, by analyzing 750 elections in 50 states from 1980 to 2008, I find that labor union density is positively associated with turnout in the American states as expected. But, the pattern appears only in midterm elections. That is, regardless of different measures of voter turnout—voter-eligible population (VEP) and voting-age population (VAP)—labor unions boost turnout in midterm elections. In contrast, they do not have mobilizing effects in presidential elections. This may be because voters have low interests and low information in midterm elections compared to presidential elections (Grummel 2008; Smith 2001). In other words, the former has narrower scope of conflicts than the latter, in the language of Schattschneider (1960), and accordingly leads to weak mobilizing force.

Second, more importantly, my multilevel analysis using the Cooperative Congressional Election Study (CCES) from 2006 to 2019 demonstrates that the positive relationship between labor union membership and electoral participation comes primarily from indirect mechanisms—nonmember mobilization (the individual-level) and aggregate mobilization (the state-level). Different from most previous studies which have focused on the direct mobilization, my findings suggest that nonmember mobilization such as family members and aggregate strength are more responsible, than member mobilization, for the decreasing levels of voter turnout in recent decades due to declining labor union membership. Therefore, this study reveals that the direct mechanisms of labor unions are limited and, instead, that labor unions primarily mobilize citizens to go to the polls indirectly via nonmember mobilization and aggregate mobilization.

In the following section, I first discuss direct and indirect mechanisms between labor unions and voter turnout. I then discuss data and methods before presenting empirical analyses. In conclusion, I summarize the main findings of the study, discuss its implications, and suggest directions for future research by considering limitations of this study.

Labor Unions and Voter Turnout: Three Mechanisms

In addition to diverse factors affecting voter turnout such as registration/voting rules (Alvarez and Ansolabehere 2002; Leighley and Nagler 2014), direct democracy (Smith 2001; Tolbert, Grummel, and Smith 2001), legislative professionalism (Percival et al. 2007), and economic and sociodemographic backgrounds (Hill and Leighley 1999; Rosenstone 1982; Schlozman, Brady, and Verba 2018; Tolbert and Hero 1996), labor unions are also considered an important mobilizing factor in American politics. Given that labor unions are a contextual variable (e.g., Frymer and Grumbach 2021), there are different theoretical mechanisms through which they can promote political participation because they need to adapt to the constantly changing political and social environments. In this section, I discuss three mechanisms: direct member mobilization (the individual-level), indirect nonmember mobilization (the individual-level), and indirect aggregate strength (the state-level).

Direct Member Mobilization

The first mechanism is direct mobilization via membership effects. Because organizations can mobilize their members through both the top-down and the bottom-up (Ahlquist and Levi 2013; Leighley 1996), it is useful to discuss both the incentives and roles of union leaders and benefits of members from the organizational structure of unions. First, because union leaders have strong incentives to achieve organizational goals, they need to directly contact their members and encourage them to take action (Rosenstone and Hansen 2003). The traditional literature on group organization explains that group participation provides three different types of benefits: material, solidarity, and purposive benefits (Clark and Wilson 1961; Salisbury 1969). While material benefits refer to personal and tangible rewards, solidarity and purposive benefits are intangible and suprapersonal. As union leaders are responsible for expanding their organizations and increasing policy benefits such as better rights and wages, they have strong incentives to directly mobilize their members for the latter benefits. It is indeed known that the presence of union leaders who are motivated to achieve their political objectives leads to more sustained and effective member mobilizations (Ahlquist and Levi 2013).

To raise solidarity benefits, leaders can hold frequent meetings and sponsor other types of gatherings where members share group membership and group identity. With the strengthened solidarity, they can in turn directly contact their members via mailings, phone calls, or mobilization drives such as door-to-door canvasses to achieve purposive benefits in electoral and/or policy-making process (Rosenstone and Hansen 2003). They also can make a public endorsement of their preferred candidates. For example, the Retail, Wholesale and Department Store Union (RWDSU), which represents about 10,000 workers in New Jersey, publicly endorsed the state Governor, Phil Murphy, to encourage their members to go to the polls and vote for him. ¹ In short, union leaders mobilize their base to achieve policy goals that they pursue (purposive benefits)—not only monetary benefits of unions, but also sometimes social and political objectives (Ahlquist and Levi 2013)—by promoting group membership and identification among the rank and file (solidarity benefits) in elections.

Second, as the bottom-up process of the direct mechanism, union rank and file can enjoy benefits from the organizational structure. Labor unions, as typically federated organizations, can allow their members to contact each other and to share information and other resources across space and even time periods (Hertel-Fernandez 2018; Kim and Margarlit 2017; Mutz and Mondak 2006). Though various types of organizations including not only labor unions but also churches and voluntary associations provide members with a context for political interactions (Verba, Schlozman, and Brady 1995), it is known that the organizational structure of labor unions is more likely to facilitate political discussions than other organizations because they encourage the discussion on issues related to their workplace via meetings, workshops, conventions, and other gatherings as noted earlier (Ahlquist and Levi 2013; Macdonald 2019).

Indeed, unions can encourage rank-and-file members to devote their attentions to obtaining policy-related information (Ahlquist and Levi 2013). Also, because union membership is helpful to increase of political knowledge (Iversen and Soskice 2015), union rank and file can reduce costs of voting and, accordingly, go to the polls more easily. Furthermore, given that the informing process can compensate for the lack of political resources, union mobilization via disseminating information and campaign activities is expected to be even more beneficial to electoral participation of the rank-and-file members, who usually lack resources otherwise (Kim 2016; Lamare 2010; Leighley and Nagler 2007; Rosenfeld 2014; Verba, Schlozman, and Brady 1995).

In a similar vein, labor unions can promote civic skills, social capital, and political efficacy. Union members can experience various intragroup activities such as electing leaders, making and following rules, and taking roles in the unions (Radcliff 2001; Zullo 2004), which raise psychological resources such as civic skills for electoral participation. In these activities, members should interact with their colleagues and, accordingly, they can increase social capital as well (Putnam 1993). Likewise, labor unions affect members’ political efficacy (Campbell et al. 1960). On the one hand, as the above mentioned intragroup activities allow members to experience democratic process, they can understand being a democratic citizen and its roles and thus increase internal efficacy. On the other hand, it is well known that unions have strong policy incentives, and also possess abundant political resources such as historical alliance with the Democratic Party (Frymer and Grumbach 2021; Rosenfeld 2014). Thus, when they are successful in achieving their policy goals via lobbying activities in policy-making process (Baumgartner et al. 2009; Denzau and Munger 1986; Gordon 2001; Hall and Wayman 1990), it can directly enhance external political efficacy of the members to actively participate in political actions (Ahlquist and Levi 2013).

Indirect Nonmember Mobilization

In addition to the direct effects, there is another way that labor unions have an impact on voter turnout indirectly. Because organizations are a linkage between the personal world and the public world, the mobilization efforts of labor unions can extend far beyond their members via social networks. That is, “leaders need not communicate with every person directly. Instead, leaders contact their associates, associates contact their colleagues, colleagues contact their friends, families, and coworkers” (Rosenstone and Hansen 2003, 27). Because union leaders seek to maximize their political and economic interests in policy-making process, they can enjoy reduced costs of mobilization by strategically engaging in nonmember mobilization using membership in social networks (Lamare 2010; Leighley and Nagler 2007; Lyon and Schaffner 2020; Radcliff 2001).

In particular, because family members are very interactive each other in our everyday lives, it is easy to share political and economic interests and deliver relevant information and sources in household (Sinclair 2012). Traditional theories of political attitudes also explain that individuals begin to shape their political preferences in their household, and political resources for participation are transmitted through family members (Schlozman, Brady, and Verba 2018). Thus, it is expected that, when a union member is aware of the roles of unions and what to do as a member in the coming election, his or her family members are more likely to learn about their roles and the issues in the election. As a result, they are more likely to participate in elections as a result of social networks (e.g., Lyon and Schaffner 2020).

In a similar vein, whenever union members need human and financial supports for their activities, they are likely to mobilize their families and close friends because they are easily contactable. Indeed, it is well known that organizing nonmembers such as families and friends has become a common strategy adopted by union-affiliated groups such as AFL-CIO’s Working America.

Indirect Aggregate Strength

As another indirect mechanism, labor unions can exert influence of indirect aggregate mobilization. This mechanism is based on their aggregate strength in the states. It is known that when unions are stronger and more pervasive in a given state, the state is likely to have less business-friendly policies (Witko and Newmark 2005), more liberal public policies (Radcliff and Saiz 1998), more equal income distribution (Bucci 2018; Rosenfeld 2014; Volscho and Kelly 2012), more equal political representation (Flavin 2018; Rosenfeld 2014), and less poverty (Brady, Baker, and Finnigan 2013). These findings suggest that labor unions may also have indirect state-level effects on political participation (Leighley and Nagler 2007; Lyon and Schaffner 2020).

Specifically, the indirect aggregate strength of unions may arise through two ways. First, because unions pursue policy benefits, where labor unions are widespread, union-friendly issues are more likely to be salient and accordingly candidates and parties are likely to have stronger incentives to be responsive to them. Thus, during election campaigns, these issues are likely to attract not only union members but also nonunion members who share similar interests in states (Leighley and Nagler 2007; Rosenstone and Hansen 2003). In this sense, nonmembers can be mobilized as they can easily obtain relevant information about the issues and become interested in the elections (Kim 2016; Lyon and Schaffner 2020; Macdonald 2019).

Second, when labor unions are stronger and more pervasive, it is also expected that electoral contests become more competitive. As labor unions emphasize pro-labor issues and promote pro-union candidates in elections, opposing candidates and parties who support business-friendly policies are likely to raise anti-labor issues and mobilize voters who have political and economic interests against labor unions. In other words, as labor unions not only emphasize pro-labor issues but also provide strong signals to individuals with anti-labor interests, they can help voters to recognize big differences between candidates or parties. Thus, the big differences in policies and candidate/party positions lead to higher voter turnout of both union members and nonmembers (Leighley and Nagler 2014; Rosenstone and Hansen 2003).

Based on the discussions above, scholars have provided empirical evidence that labor unions are positively associated with voter turnout rates (Leighley and Nagler 2007; Radcliff 2001; Radcliff and Davis 2000). However, they have several analytical limitations. First, because Radcliff (2001) and Radcliff and Davis (2000) do not consider state-level effects in their individual-level analyses, their findings suffer from omitted variable bias. As Leighley and Nagler (2007) adequately point out, union strength can be correlated with unmeasured attributes of each state and, thus, the state or local level analysis may be more appropriate to examine the impact of labor unions on voter turnout. Moreover, given the fact that unions and their relationship with governments are different across industries, countries, and time periods (Ahlquist 2017), the American states, which embody an appropriate condition for “the controlled experiment” (Gray, Hanson, and Kousser 2018, xi), would also provide analytical benefits to examine the relationship between unions and turnout.

Second, however, though Leighely and Nagler (2007) adopt more appropriate empirical models and provide more robust findings using the state-level data, they also suffer from misspecification. Specifically, they only consider union membership at the individual-level and union density at the state-level by just assuming that the latter “encompasses the nonmembership effects” (433). But, according to the theories above, there are three different mechanisms through which labor unions affect voter turnout: direct member mobilization (the individual-level), indirect nonmember mobilization (the individual-level), and indirect aggregate strength (the state-level). Previous studies do not carefully consider all of the three mechanisms, but examine only two of them (usually, the first and the third mechanisms). Therefore, I examine the three theoretically relevant mechanisms in my empirical models to provide more robust findings of the relationship between labor unions and voter turnout.

Before describing my data and model specification at both the state-level and the individual-level, I briefly discuss political ideologies of labor unions and how those ideologies have evolved in recent years. It is well known that the organized labor traditionally has close organizational ties with the Democratic Party (Frymer and Grumbach 2021; Greenstone 1977; Rosenfeld 2014). However, because labor unions have sometimes failed to successfully achieve their legislative goals, some describe the ties as one-sided partnership (Francia 2010). Moreover, due to the election of Donald Trump, labor unions—especially, white working class—may be regarded as pro-Republicans at least in some regions (Devinatz 2017; Francia 2020). ² However, despite the recent dynamic evolution of labor unions’ political ideologies, I do not expect my analyses suffer from severe biases. First, theoretically, because I examine voter turnout, not vote choice, their political ideologies would not bias my analyses. Second, empirically, because I include the 50 states and multiple years in the analyses, I can control for state- and/or year-specific effects.

Empirical Analysis

State-Level Analysis

For the state-level analysis, I collect data on voter turnout in all of the 50 states from 1980 to 2008. ³ The choice of time period is data-driven rather than theory-based. This yields a dataset of 750 elections from 50 states, with 15 elections in each state. My dependent variable is VEP turnout. Though there is a debate upon appropriate measurement for voter turnout, VAP turnout may lead to downward bias because it includes varying alien populations who cannot vote (Blais and Dobrzynska 1998). In contrast, the VEP turnout purely calculates the percentage of eligible voters by excluding noneligible populations such as felons and noncitizens. Thus, it is regarded as the more accurate measure of turnout rates (Macdonald 2021; McDonald and Popkin 2001). Therefore, I use the VEP turnout rates in the models below. ⁴ I obtain the data from the website of United States Elections Project (McDonald 2020).

Also, it should be noted that as the time period in the study is from 1980 to 2008, it includes both presidential elections and midterm elections. Previous studies suggest that presidential and midterm elections should be treated separately (Grummel 2008; Jackson 1997; Smith 2001; Tolbert and Smith 2005). This is because factors that affect voter turnout are different in presidential and midterm elections (Rosenstone and Hansen 2003). That is, as presidential races already provide voters with a strong incentive to vote, turnout in presidential elections is higher than in midterm elections. Even though adding mobilization factors driving voter turnout should increase benefits of voting, the pattern of diminishing returns appears in presidential elections. That is, “the larger the benefits already gained from voting, the weaker the stimulus to turnout” (Smith 2001, 701). Therefore, I provide three separate models: midterm election, presidential election, and pooled models. I expect that the variable of interest, union mobilization, will be weakly or not significant in pooled models and presidential election models, while it will be significant in midterm election models. ⁵

My independent variable is union mobilization. For its measurement, I draw data on union membership density from the website of Union Membership and Coverage Database from the CPS (Hirsch and Macpherson 2020). ⁶ Additionally, I include controls that have been found to affect voter turnout in American contexts. First, I include institutional and political variables in models. Following Grummel (2008) and Tolbert, Grummel, and Smith (2001), I measure registration requirements as the number of days before the election a voter can register to vote in each state over time. For example, I coded 0 if states have the Election Day registration, and coded 30 if states require voter registration a month before the election.

I also control for electoral competition in states. It is expected that highly competitive elections incentivize voters to go to the polls because they can expect their votes to be more decisive and valuable (Engstrom 2012; Jackman 1987; Powell 1986). Holbrook and Van Dunk (1993) offered the measure of electoral competition based on district-level state legislative elections in 1980s, and Shufeldt and Flavin (2012) updated the data based on elections since 1990s. Thus, I obtain the data from both Holbrook and Van Dunk (1993) and Shufeldt and Flavin (2012) for time period before and after 1990, respectively. It ranges from 0 to 100, and higher values mean greater competition. As direct democracy influences voter turnout, I control for effect of initiative and referendum. I obtain the information on initiative and referendum from Initiative and Referendum Institution at the University of Southern California. States with statewide initiative or referendum are coded 1, and otherwise 0. Because professionalized state legislatives are likely to address higher political stakes which drive voter turnout, I control for professionalization score developed and measured by Squire’s (2017) index. It ranges from 0 to 1.

To control for economic and sociodemographic factors, I first include economic condition of states, which is measured by Gross State Product (GSP) growth rate from Bureau of Economic Analysis. Second, to account for education, the proportion of the population with a high school degree or higher in each state is included, which is from U.S. Department of Commerce. Third, the proportion of population residing in urban areas and median age of population in each state are included (Grummel 2008; Jackson 1997). Fourth, because race is another important factor (Hill and Leighley 1999; Leighley and Nagler 2014), I control for minority diversity index, which has been used by prior studies (Grummel 2008; Tolbert and Hero 1996). Lastly, the models contain the following dummy variables: southern state, presidential election, senate election, gubernatorial election. The summary statistics of all variables in the analysis is presented in Supplementary Appendix A.

Because I use time-series cross-sectional data, which covers 50 states from 1980 to 2008, ordinary least squares (OLS) regression is not appropriate due to the data structure. This is because error terms in regression equations cannot be independent, which violates an OLS regression assumption and causes autocorrelations. Moreover, since the data include more panels (N = 50) than time points (T = 15), statistical issues of heteroskedasticity and serial correlation across panels should be addressed. Even though estimated coefficients may not be biased under OLS regressions, the analyses will suffer from inefficient and biased standard errors. In order to address the issues, I utilize panel corrected standard errors (PCSE) as Beck and Katz (1995) recommend. At the same time, I also include a lagged dependent variable (LDV) to allow for temporal dynamics with AR(1) process. In particular, the inclusion of LDV is beneficial both theoretically and methodologically. In a theoretical sense, variation of voter turnout is a dynamic process such that the past turnout in a state is related to the current turnout in the state. In addition, methodologically, the inclusion of LDV can make models avoid omitted variable bias and mitigate problems related to unit heterogeneity. Indeed, when specifying dynamic models for dynamic theories, it is more appropriate to include LDV in models (De and Keele 2008; Keele and Kelly 2006). However, in addition to this specification, I also report results from two-way fixed effects (2FE) models with robust standard errors clustered by state. Because it is expected that the 2FE models make the standard errors a little bit larger and remove all observed and unobserved time-invariant differences across states, they can be a much stronger specification. ⁷

State-Level Findings

Table 1 shows empirical findings from the three separate state-level models (midterm election model, presidential election model, and pooled model) as well as from the 2FE models.

Table 1. State-level analysis: Labor union and voter turnout (VEP)

Note. Nonstandardized coefficients and panel corrected standard errors are presented in Model 1–3. Nonstandardized coefficients and robust standard errors clustered by state from two-way fixed effects models are reported in Model 4. Significance level: **p < 0.01 and *p < 0.05 (two-tailed).

Model 1 depicts the relationship between union mobilization and voter turnout in midterm elections. Because voters tend to have lower information and interests in midterm elections due to narrower scope of conflicts compared to presidential elections (Grummel 2008; Schattschneider 1960; Tolbert and Smith 2005), it is expected to observe a statistically significant and positive coefficient estimate on the union membership density variable. As expected, the coefficient is in the expected direction and statistically significant. This clearly reconfirms that, while controlling for other variables, labor union membership density is positively associated with voter turnout (Leighley and Nagler 2007; Radcliff 2001).

Substantively, this effect indicates that if the union membership density is 32.1% (e.g., highest; HI in 1982) compared to 3.3% (e.g., lowest in the data; NC in 2006 and SC in 2006), the voter turnout increases by about 7% point in midterm elections given the previous level. Also, if the density is 21.3% compared to 7.7% (one standard deviation above and below the mean value, 14.5%, in midterm elections), the voter turnout is expected to increase by about 3.3% point given the previous level.

While there is a significantly and substantively significant impact of the labor union membership density in midterm elections, labor unions are not related to voter turnout rates in presidential elections. Model 2 displays the association between union mobilization and voter turnout in presidential elections. Following the discussion above, it is expected that the mobilizing force of unions may be insignificant due to the diminishing returns, which suggest “the larger the benefits already gained from voting, the weaker the stimulus to turnout” (Smith 2001, 701). Indeed, the coefficient of the union membership density is not statistically significant in Model 2. The similar pattern is observed in Model 3, where both midterm and presidential elections are pooled. As the statistically and substantively significant coefficient of the presidential election dummy variable shows, union mobilization does not have additional driving forces for electoral participation when voters already have strong incentives to participate in presidential elections, which have higher stakes of interest through broader scope of conflicts (Schattschneider 1960).

In order to visually display the findings in Table 1, I pool both midterm and presidential elections in one model by creating an interaction term between union membership density and presidential election dummy variable. The models are reported in Supplementary Appendix D, from which I draw Figure 1. The vertical axis in the figure indicates the predicted values of turnout measured by VEP (left panel) and VAP (right panel) across different levels of union membership density on the horizontal axis.⁸ I again confirm the patterns of the relationship that are different between midterm and presidential elections. Both VEP and VAP increase as union membership density increases in midterm elections, whereas the pattern is not observed in presidential elections. Thus, it reveals that the mobilizing force of labor unions is limited to the former.

Figure 1. Labor union and voter turnout (VEP and VAP).

Note. Predicted values of voter turnout (solid lines) are from pooled interaction models in Supplementary Appendix D. Dashed lines indicate the 90% confidence intervals.

When it comes to the LDV and control variables in Table 1, there is little difference between midterm and presidential elections. Previous turnout, the LDV, is statistically significant in the expected positive direction, which shows its temporal dependence. Voter registration requirements have significant and negative coefficients, suggesting that, as previous studies demonstrate, voter turnout becomes higher as a state has generous registration rules such as the Election Day registration (Alvarez and Ansolabehere 2002; Leighley and Nagler 2014). Electoral competition and direct democracy are also statistically significant and positive as expected. That is, higher level of electoral competition, especially in the district-level, leads to higher voter turnout in states. Likewise, states with statewide initiative or referendum are more likely to have higher turnout. Interestingly, though legislative professionalism is statistically significant, it is negative in midterm elections but positive in presidential elections. Due to the inconsistent directions of the impact, it is not significant in the pooled models.

Regarding economic and sociodemographic variables, GSP growth rate has significant and negative coefficients in the three models. This supports the negative relationship between economic conditions and voter turnout (Kern, Marien, and Hooghe 2015). In other words, American voters are more likely to go to the polls in economic hardships. While education and age are not significant, urbanization and minority diversity have statistical significance. But, the former has a negative and significant coefficient only in midterm elections, whereas the latter does only in presidential elections.

In additional analysis with alternative specifications, I checked the robustness of the findings by using the 2FE models, operationalizing the dependent variable using the VAP instead of VEP, and dropping the LDV and instead including state dummy variables. None of these alternative specifications, as reported in Model 4 and Supplementary Appendices B and C, produced qualitatively different findings.

Individual-Level Analysis

As previous studies have demonstrated (Kim 2016; Lamare 2010; Leighley and Nagler 2007; Radcliff 2001), my state-level analysis in the previous section clearly shows that labor unions are positively associated with voter turnout. However, it reveals that the impact of labor unions is observed only in midterm elections, but not in presidential elections, because of the pattern of diminishing returns (Smith 2001). In this section, more importantly, I further examine whether the impact is direct via member mobilization or indirect via nonmember mobilization. As noted earlier, though previous studies find a positive relationship between labor unions and political participation, they do not carefully examine whether the relationship comes primarily from direct member mobilization (the individual-level), indirect nonmember mobilization (the individual-level), or indirect aggregate strength (the state-level).

To address the existing analytical limitations, I test the individual-level mechanisms using the cumulative CCES data (2006–2019) (Kuriwaki 2020). ⁹ Despite its online survey format, the primary reason that I use the CCES, rather than the ANES, is that union capacity to mobilize voters relies more on the state or local context than on the national context (Leighley and Nagler 2007). Thus, I expect the data to provide analytical benefits with more respondents from each state who are surveyed around November of each year.

My dependent variable in the individual-level analysis is voter turnout. To measure respondents’ participation in the elections, pollsters directly asked whether they participated in the elections or not. If a respondent participated, I score him or her 1 on this measure, and 0 if otherwise. To examine different mechanisms of the impact that labor unions have on voter turnout, three measures are employed as independent variables: (a) whether a respondent is currently a member of a union (direct member mobilization); (b) whether any member of a respondent’s household is currently a member of a union (indirect nonmember mobilization) ¹⁰; and (c) state union membership density (indirect aggregate mobilization). The first and second individual-level variables are measured as binary variables, while the third state-level variable again comes from Union Membership and Coverage Database from the CPS as (Hirsch and Macpherson 2020).

Apart from the independent variables, political and sociodemographic covariates are included in the analysis: political ideology (1 = “very liberal”; 3 = “very conservative”); partisan strength (1 = “independent”; 3 = “strong partisan”); income (1 = “first quintile”; 5 = “fifth quintile”); education (1 = “≤high school graduation”; 2 = “two-year college”; 3 = “four-year university”; 4 = “graduate”); gender (1 = “female”; 0 = “male”); age and its squared term; race (White, Black, Hispanic, and others); marital status (1 = “married”; 0 = “not married”). I also include the presidential election dummy variable. The descriptive statistics of all variables in the analysis is presented in Supplementary Appendix E.

Because the dependent variable is a binary variable, binary logistic regression models should be utilized. And, the year fixed effects should be considered to control for the influence of unique variables of each year that might affect the dependent variable though not included in the models. However, more importantly, I try to examine the effect of labor unions operationalized by three different measures. Yet, the state union membership density does not vary across individuals in a given state. This implies that there are two nested levels in the data: individuals (level 1) and states (level 2). If the empirical models fail to recognize the multilevel data structure, the results suffer from severe bias due to the violation of the assumption of independent errors (Raudenbush and Bryk 2002; Steenbergen and Jones 2002). To avoid the bias, I estimate hierarchical binary logistic regression models. In addition to the multilevel approach, I here again report results from 2FE models with robust standard errors clustered by state.

Individual-Level Findings

Is the impact of labor unions direct via member mobilization or indirect via nonmember mobilization? Table 2 presents the results from the multilevel models. Model 5 and Model 6 examine whether being a union member or having family members who belong to the unions is more likely to participate in elections, respectively. As shown in the models, the empirical findings provide the evidence that both have mobilizing effects. The coefficients of the variables of interest are statistically significant in positive directions while controlling for the state-level union density, which also has statistical significance in a positive direction as expected (indirect aggregate strength).

Table 2. Individual-level analysis: Direct and indirect mobilization (CCES)

Note. Coefficients and standard errors from multilevel logistic regression models are presented in Model 5–7. Coefficients and robust standard errors clustered by state from binary logistic regression models with two-way fixed effects are reported in Model 8. Significance level: **p < 0.01 and *p < 0.05 (two-tailed).

Substantively, according to Model 5, when an individual is a member of labor unions, the probability of his or her voting increases by about 4.7%. Likewise, in Model 6, when having family members who belong to labor unions, the predicted probability of voting increases by about 6.6%. Therefore, it seems that the impact of labor unions on political participation comes from both direct member mobilization (the individual-level) and indirect nonmember mobilization (the individual-level).

However, the third column of Table 2, where the two variables of interest are included at the same time in one model, shows interesting results. In Model 7, while having family members who belong to labor unions remains still significant in a positive direction, being a labor union member does not hold statistical significance anymore. The state-level union density is still controlled for in the model and, it has a positive and significant coefficient. In other words, when controlling for the indirect nonmember mobilization and the indirect aggregate strength of labor unions, the direct member mobilization does not drive voter turnout.

The results contradict the findings in previous studies that both the direct member mobilization and the state-level union membership density boost electoral participation (Kim 2016; Leighley and Nagler 2007; Radcliff 2001). However, while they cannot directly compare the impacts of member and nonmember mobilization because of the omission of the indirect nonmember mobilization in their empirical models, the results in Model 7 of Table 2 enable the comparison. And it clearly shows that being a member of labor unions is not associated with turnout when indirect nonmember mobilization is appropriately controlled for. Instead, having family members who belong to labor unions is positively related to voter turnout. That is, substantively, when at least one of family members is a union member, the probability of voting increases by about 5.8%. This suggests that labor unions’ positive impact does not come from the direct member mobilization, but from the indirect nonmember mobilization and the indirect aggregate strength of labor unions. Put differently, the primary reason that declining union membership reduces the voter turnout rates in the US is not direct mobilization, but indirect mobilization. ¹¹ And I obtain similar results from Model 8 which includes state and year fixed effects (2FE) with robust standard errors clustered by state.

The control variables in the models of Table 2 have significant coefficients, and they are not qualitatively different across the models. As individuals have liberal ideologies, they are more likely to participate in elections. As expected, partisan strength, income, education, and marriage are positively associated with voter turnout and, racial minorities such as blacks and Latinos are less likely to participate than whites. Also, female is less likely to go to the polls compared to men, and both age and its squared term are statistically significant in the expected direction. As the state-level findings show in the previous section, both presidential election and state-level union membership density have a positive association with voter turnout.

Conclusion

Scholars have been interested in labor unions as a key institution that not only shapes political and policy attitudes of their members (Frymer and Grumbach 2021; Hertel-Fernandez 2018; Kim and Margarlit 2017; Mutz and Mondak 2006), but also mobilizes their members in elections (Leighley and Nagler 2007; Radcliff 2001; Rosenfeld 2014). However, prior studies have paid particular attention to direct mechanisms through which unions exert their mobilizing influence. As a result, we have relatively little understanding of indirect mechanisms between unions and voter turnout. Given the fact that there are three theoretical mechanisms between them as discussed above, previous studies that usually examined direct member mobilization and indirect aggregate strength—without careful consideration of indirect nonmember mobilization—may suffer from analytical limitations (Leighley and Nagler 2007; Radcliff 2001). Moreover, the fact that union membership has kept decreasing in recent decades implies that it might not be enough for union leaders to mobilize only their members via direct mobilization. In other words, the decreasing trends of union membership raise an important question of whom and how labor unions mobilize to overcome changing environments. In this paper, I therefore examined all the three direct and indirect mechanisms using newly updated data.

To do this, I analyzed both state-level panel data and individual-level survey data with multilevel approach. First, according to my state-level analysis using 750 elections which cover the 50 states from 1980 to 2008, I find that union mobilization is positively associated with voter turnout as demonstrated by previous studies. However, the positive relationship is observed only in midterm elections, but not in presidential elections. This implies that the mobilizing force that labor unions have is limited to midterm elections, where voters enjoy relatively lower levels of interests and information compared to presidential elections. This is because, in the language of Schattschneider (1960), the scope of conflicts in midterm elections is narrower than that of presidential elections. Put differently, given the fact that presidential elections already provide voters with strong incentives to cast a ballot (Smith 2001; Tolbert and Smith 2005), it shows that additional mobilizing efforts such as union mobilization cannot boost voter turnout due to the pattern of diminishing returns.

In addition to the state-level evidence, my individual-level analysis shows that labor unions indeed play an important role in promoting electoral participation in the states. Interestingly, however, unlike prior studies (Leighley and Nagler 2007; Radcliff 2001), when considering its three different mobilizing mechanisms, the positive impact that labor unions have on voter turnout does not come from the direct member mobilization, but primarily from the indirect nonmember mobilization and the indirect aggregate strength. This may indicate that the primary reason of declining voter turnout due to weakening union membership in the states is not direct mobilization, but indirect mobilization.

Given the fact that membership of organizations including labor unions has kept decreasing recently, my findings imply that it can be more important to consider indirect mobilization for political participation. As discussed earlier, the indirect mechanisms primarily include social ties and aggregate strength (Kim 2016; Leighley and Nagler 2007; Lyon and Schaffner 2020; Radcliff 2001). That is, individuals who have social ties to union members can enjoy both relevant information and recruitment opportunities. Likewise, when living in a state where labor unions are more pervasive, people are likely to experience elections with salient issues and thus obtain relevant information and opportunities to be recruited. Therefore, when union leaders pursue their political and economic goals in policy-making process, they need to devote more attention to strategies of indirect mobilization not only in elections but also in other types of participation. Also, beyond labor unions whose membership has been declining in recent decades, alternative institutions which can play similar roles in disseminating information through networks and making issues salient in elections are necessary to increase voter turnout in the states.

In a broader sense, unions’ successful strategies of indirect mobilization would be much more beneficial to our political community. Scholars explain that because the goals of labor unions are closely related to public policies that citizens with low socioeconomic status tend to support, political results such as more liberal policies (Radcliff and Saiz 1998), more equal income distribution and political representation (Bucci 2018; Flavin 2018; Rosenfeld 2014; Volscho and Kelly 2012) are likely to be accomplished by unions. Thus, when their indirect strategies are successful by mobilizing nonmembers as well as members, their roles in increasing political and economic equality will become more active. That is, labor-friendly policies such as more redistributive policies, more generous healthcare, a higher minimum wage, and a more progressive taxation are likely to be implemented to offset business-friendly policies. If this is the case, unions, despite continuously decreasing trends of membership, can help reduce economic and political inequality via indirect mobilization.

However, it should be noted that though my findings contradict direct impact of unions on turnout in the states, it does not necessarily mean that there is no direct impact on their members at all. As scholars have explained (Ahlquist 2017), labor unions are heterogeneous not only across countries and time periods but also across industries and sectors even within a country. For example, despite the decreasing levels of union membership in recent decades, the degree of decrease is different between private- and public-sector in the US. Moreover, member characteristics such as education and income levels are different as well across industries and sectors (Rosenfeld 2014). This implies that each union leader may have different incentives and strategies depending on their external and internal environments, which in turn affect their mobilizing strategies (e.g., direct vs. indirect). For example, Hertel-Fernandez, Naidu, and Reich (2021) analyze teacher unions, one of public-sector workers, and find that teacher strike leaders successfully mobilized their members. Therefore, because direct mobilization may be still more useful and powerful in some types of unions, future research should analyze how the mobilizing mechanisms are different across industries and sectors.

Furthermore, when looking beyond unions’ impact on political participation, their influence on rank-and-file members is also observed in shaping policy and political attitudes. Though my findings suggest that unions exert their mobilizing force primarily through indirect mechanisms in elections, scholars demonstrate that union membership directly reduces racial resentment (Frymer and Grumbach 2021) and shapes policy preferences of their members (Ahlquist, Clayton, and Levi 2014; Hasenfel and Rafferty 1989; Kim and Margarlit 2017). On the one hand, this certainly suggests that unions’ direct impact can be a primary mechanism in shaping policy preferences and political attitudes. However, on the other hand, because prior studies have not directly examined to what extent and in what way unions exert indirect influence in shaping those preferences, future studies need to analyze the degree and way of the indirect mechanisms in policy areas as well.