This paper offers empirical evidence on the impact of trade unions on wage inequality in Mexico. The results indicate that unions were a strongly equalizing force affecting the dispersion of wages in 1984, but were only half as effective at reducing wage inequality in 1996. Not only did the unionized percentage of the labor force fall considerably over the period, unions also lost some of their ability to reduce wage dispersion among the workers they continued to represent. Had unions maintained in 1996 the same structural power they possessed in 1984, the rise in wage inequality in the formal sector of the labor market between those years would have been reduced by roughly 11%.