Trade union institutions are historically and comparatively weak in the United States, and union membership has been in steady decline over several decades. Scholars thus question the contemporary relevance of organized labor to social policy. Yet, there is considerable state-level variation in social policy and union institutional strength that remains underexamined. Focusing on variability across US states, this paper uses mixed-methods analysis to examine relationships between organized labor and parental and family leave legislation under varying political conditions. Event history analysis of state-level leave policy adoption from 1983 to 2016 shows that union institutional strength, particularly in the public sector, is positively associated with the timing of leave policy adoption. These findings are robust to the inclusion of other factors, including Democratic control of state houses, which is also shown to facilitate leave policy adoption. Comparative case studies support event history findings and illustrate how state house partisanship informs the level of government that leave advocates target for policy change. The paper concludes by suggesting further attention to subnational policies and investigation into the social movement practice of target-shifting and its effects. Ultimately, the paper demonstrates the operation of power resources at the subnational level within a liberal market national context.