We study the role of union heterogeneity in shaping wages and inequality among unionized workers. Using linked employer-employee data from Brazil and job moves across multi-firm unions, we estimate over 4,800 union-specific pay premia. Unions explain 3–4% of earnings variation. While unions raise wages on average, the standard deviation in union effects is large (6-7%). Validating our approach, wages fall in markets with higher vs. lower union premia following a nationwide right-to-work law.