An enduring puzzle in the study of American public opinion is what explains the decline in citizens’ trust in government since the late 1960s. We contribute to the study of trust by examining a factor that has received little attention to date: the adoption of public sector collective bargaining laws by U.S. states. We theorize that the widescale unionization of public employees is likely to negatively impact trust in government because it leads to a decline in political authority, accountability, and government responsiveness. Using American National Election Studies (ANES) data to measure citizens’ trust in government consistently over time, we leverage differences in the timing by which states adopted collective bargaining laws for public sector workers across a variety of occupations (state employees, local employees, teachers, police officers, and firefighters). We find consistent evidence that citizens report lower levels of trust in government after their state adopts public sector collective bargaining and this finding is robust to a variety of subsample analyses as well as timing and placebo checks. Notably, we also find a similar effect when assessing 1972-1976 ANES panel data, a timeframe when several states enacted these laws. Our findings have important implications for our understanding of the decline in citizens’ trust in government as well as changing the focus of the literature on public sector unions that, to date, has emphasized economic impacts.