Cross-national comparative research suggests that organized labor’s influence on U.S. social policy is unexpected. Additionally, the nation’s steady decline in union membership raises further doubts about organized labor’s relevance to contemporary politics. Yet, there has been little attention to subnational variation in social rights and union institutional strength. Focusing on U.S. states, this paper examines relationships between trade unions and workplace leave legislation under varying political conditions using event history methods. I argue that unions are relevant to state parental and family leave policies, but partisan control of state houses opens and closes opportunities for union influence. Findings are supported by two case studies that additionally show how state house partisanship shapes leave advocates’ strategies and access to government actors.