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.