Social responsibility is addressed to corporations, but can also be applied to other powerful organizations. This study tests the impact of labor union social responsibility on key measures of labor union attachment. After developing a scale of labor union social responsibility, craft union apprentice workers were surveyed and their responses analyzed with structural equation modeling. Labor union social responsibility was directly and positively related to union commitment and job satisfaction. Union commitment and job satisfaction fully mediated the negative relationship between labor union social responsibility and propensity to withdraw from the union, and the positive relationship between labor union social responsibility and union participation. The results suggest that labor union social responsibility can enhance union attachment and inform union strategy.