Using data from the European Social Survey (2002-14), this paper explores the effect of union membership on support for redistribution. We 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 our 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. We also show that low-wage workers have become a significantly less important union constituency in many European countries over the time period covered by our analysis.