Scholars and political observers point to declining labor unions, on the one hand, and rising white identity politics, on the other, as profound changes in American politics. However, there has been little attention given to the potential feedback between these forces. In this article, we investigate the role of union membership in shaping white racial attitudes. We draw upon research in history and American political development to generate a theory of interracial labor politics, in which union membership reduces racial resentment. Cross‐sectional analyses consistently show that white union members have lower racial resentment and greater support for policies that benefit African Americans. More importantly, our panel analysis suggests that gaining union membership between 2010 and 2016 reduced racial resentment among white workers. The findings highlight the important role of labor unions in mass politics and, more broadly, the importance of organizational membership for political attitudes and behavior.