Existing studies of ethnic voting mainly focus on democratic elections. In electoral autocracies, politically subordinate ethnicity can help citizens coordinate against the incumbent. However, we argue that collective action will be constrained when the group grows large, as it becomes costly for its members to form common behavioural norms and carry out effective sanctions through shared ethnic ties under authoritarian repression. Drawing on unique historical surveys in Taiwan, we study how Taiwanese ethnicity and local ethnic demography jointly induced voters' defection against the hegemonic KMT regime. We find that the pro-defection or anti-incumbent effect of Taiwanese ethnicity fell as the share of Taiwanese citizens in a township increased. However, the relative size of the Taiwanese group no longer undermined pro-defection ethnic voting after the KMT lifted the ban on opposition parties. Our results illustrate that formal organizations play a critical role in sustaining the informational salience of ethnicity in the elections.
