Women have long been underrepresented in American politics. This is evidenced by women being less likely to run for and hold elected office. Existing scholarship largely focuses on explaining why women are less politically ambitious than their male counterparts but pays less attention to why some women do run for office. To this end, I focus on the potential role of labor union membership. I argue that labor unions can foster political ambition and increase ordinary people’s likelihood of running for office. I test this among women in the American mass public, primarily with survey data from the 2010–22 Cooperative Election Study (CES). Overall, I find that labor union membership is significantly associated with women’s likelihood of running for office. I also find that this robust relationship is unlikely to be driven by self-selection or omitted variable biases. Overall, these findings help us to better understand the sources of political ambition, illustrate a viable potential pathway to boost women’s likelihood of seeking elected office, and underscore the political consequences of organized labor.