Using data from the European Social Survey (2002–14), this article explores the effect of union membership on support for redistribution. The authors hypothesize that the wage-bargaining practices of unions promote egalitarian distributive norms, which lead union members to support redistribution, and that this effect is strongest among high-wage workers. Consistent with the authors’ expectations, the empirical analysis shows that the solidarity effect of union membership is strongest when unions encompass a very large share of the labor force or primarily organize low-wage workers. The authors also show that low-wage workers have become a significantly less important union constituency in many European countries over the time period covered by the analysis.