The minimal effects of union membership on political behavior

What is the source of labor unions’ power? A large literature argues that union membership powerfully affects political behavior and attitudes, in turn making unions a powerful interest group. However, union members may not receive, may ignore, and may deprioritize their union’s message compared to other considerations. Previous research faced empirical challenges with causal inference, limited sample sizes, and limited outcomes. I marshal data from 14 panel surveys from 1956 to 2022 with 48,629 respondents to help better understand the causal effects of union membership. In these data, I use difference-in-difference designs to evaluate whether gaining union membership causes voters to liberalize their attitudes and participate in politics. I do not find any evidence that union membership affects political behavior, and I show that we can reject modest effects in most cases. I also show that a prominent previous result is not robust. These results suggest a reconsideration of how labor unions influence politics.