This study investigates the employment impact which emerges from a deregulation of shop opening in the German retail sector. Exploiting the gradual change in the opening times across states difference-in-differences estimates point to an average increase in the employment probability, driven by a rise in the likelihood of working marginal part-time hours. For individuals facing high family-related supply-side constraints the change of the opening times has opposing effects on employment, positive on the lower and negative on the upper part of the hours distribution. Overall the deregulation is estimated to have raised the likelihood of underemployed work.