While the tension between political equality and economic inequality is as old as democracy itself, a recent wave of scholarship has highlighted its acute relevance for democracy in America today. In contrast to the view that legislative responsiveness favoring the affluent is near to inevitable when income inequality is high, we argue that organized labor can be an effective source of political equality in the US House of Representatives. Our novel dataset combines income-specific estimates of constituency preferences based on 223,000 survey respondents matched to 27 roll-call votes with a measure of district-level union strength drawn from administrative records. We find that local unions significantly dampen unequal responsiveness to high incomes: a standard deviation increase in union membership increases legislative responsiveness towards the poor by about 6 to 8 percentage points. We rule out alternative explanations using district fixed effects, interactive and flexible controls accounting for policies and institutions, as well as a novel instrumental variable for unionization based on history and geography. We also show that the impact of unions operates via campaign contributions and partisan selection. Our findings underline calls to bring back organized labor into the analysis of political representation.