This paper analyzes the existence and extent of downward nominal wage rigidities in the Mexican labor market using data from the administrative records of the Mexican Social Security Institute (IMSS). This establishment-level, panel dataset allows us to track workers employed with the same firm, observe their wage profiles and calculate the nominal-wage changes they experience over time. Based on the estimated density functions of nominal wage changes, we are able to calculate some standard tests of nominal wage rigidity that have been proposed in the literature. Furthermore, we extend these tests to take into account the presence of minimum wage laws that may affect the distribution of nominal wage changes. The densities and tests calculated using these data are similar to those obtained using administrative data from other countries, and constitute a significant improvement over the measures of nominal wage rigidities obtained from household survey data. We document the importance of minimum wages in the Mexican labor market, as evidenced by the large fraction of minimum wage earners and the indexation of wage changes to the minimum wage increases. We find considerably more nominal wage rigidity than previous estimates obtained for Mexico using data from the National Urban Employment Survey (ENEU) suggest, but lower than that reported for developed countries by other studies that use comparable data.