The recent reform or the labour law includes a non discrimination article that protects gender and sexual preferences.

Sources: Mexican Labour Ministry: stps.gob.mx/bp/micrositios/…

The concept has never been illegal in Mexico, but in the times of the colony by Spain, sodomy was a grave felony. Those proven guilty were burned by the Holy Inquisition. In the independent period homosexuality was an administrative felony, that was charged by the police at discretion. This practice has been waning since the arrival of the modern democracy at the beginning of the 21st century. With the broad reform about human rights the protection of sexual preference was included in the federal constitution in 2011. http://dof.gob.mx/nota_detalle.php?codigo=5194486&fecha=10/06/2011

Sources: Book: Garza, Federico. Quemando mariposas. Sodomía e imperio en Andalucia y México, siglos XVI-XVII. Laertes. Barcelona, 2002.