Bilateral bargaining between a multiple-worker firm and individual employees leads to overhiring. With a concave production function, the firm can reduce the marginal product by hiring an additional worker, thereby reducing the bargaining wage paid to all existing employees. We show that this externality is amplified when firms can adjust hours per worker as well as employment. Firms keep down workers' wage demands by reducing the number of hours per worker and the resulting labor disutility. Our finding is particularly relevant for European economies where hours adjustment plays an important role. R An earlier version of this paper was circulated under the title 'Employment, Hours and Optimal Monetary Policy'. We thank the associate editor, Antonella Trigari, and an anonymous referee for very useful comments and suggestions. We are grateful to