Labor unions are key stakeholders in the field of corporate social responsibility but researchers have paid surprisingly little attention to their CSR strategies. This article extends stakeholder theory by treating unions as having stakeholders that influence their CSR strategies. Drawing on qualitative data from a longitudinal study on selected unions in France between 2006 and 2013, this paper analyzes the underlying reasons for the differences in their approaches. It finds connections between the unions’ CSR strategy, and the perception of and cooperation with stakeholders