This study examines whether and how labor unionization influences stock price crash risk. Using a regression discontinuity design that employs union elections as an exogenous shock yielding local variation in unionization, we find that unionization leads to a significant decline in stock price crash risk. We further explore the underlying mechanisms through which unionization affects crash risk and find that labor unions constrain managerial resource diversion and overinvestment, demand less risk-taking, and facilitate transparent information flow, which in turn reduces crash risk. Overall, our results suggest that unions play an important governance role. Our study sheds new light on a formerly under-researched beneficial impact of unionization and the role that organized labor plays in influencing extreme downside risk in the equity market.