Despite an extensive literature examining the effects of unions on wages, little attention has been paid to the resultant aggregate employment consequences of this change in the relative cost of unionized labor. This article uses 1983 Current Population Survey data to estimate the effects of union strength on the probability of employment and labor force participation. Union strength, which reflects both union coverage and the union wage differential, is found to decrease employment and increase unemployment by a small but significant amount. These effects are concentrated primarily among females and young males, while little impact is found on prime-age males.

This article examines a dynamic adverse‐selection model that generates equilibrium employment cycles. In the model, firms hire workers from unemployment, observe workers' productivity through time, and (following the profit‐maximizing rule) eventually fire unproductive workers. If hiring costs are low, the dynamical system converges to a steady state in which the unemployment pool contains mostly low‐ability workers. However, if hiring costs are sufficiently large, this “lemons effect” would make firms unwilling to hire workers. In this case, the system converges to a cyclical equilibrium in which firms alternate between hiring and not hiring.