In this article, I consider how ideas and interpretive frames generated by one movement may spill over its boundaries to inspire individual members of the society to take their own action. I apply this idea to examine the role of labor unions in boosting legal mobilization among nonunion workers in the US. To do so, I constructed a new dataset of the legal cases filed by workers under the Fair Labor Standards Act (FLSA) in all 50 states in the US over a period of 25 years from 1989 to 2016. Exploiting variation in state union density during the same period, I find that an increased union density positively affects the number of cases filed by nonunion workers. This finding informs our understanding of the broader spillover effect of movements, and in turn, effect of unions outside of unionized workplaces. The finding is of particular importance as hostility towards unions grows and as labor movement seeks its revitalization through creative forms of union activism.