"LA MORDIDA", translation "the bite" is the term used for a bribe in this country. It is the traditional and customary way of getting things done. The bureaucrat who does your bidding takes a bite out of the cost of completing your objective. Mexican reformers are trying to change this condition with little success. It is so institutionalized that it could take decades before the situation changes appreciably. Bribing a cop, a judge or a permit agent is not the exclusive domain of Mexico. News stories about bribery scandals in the United States are not uncommon but in Mexico it is a way of life instead of an aberration in the system. Source
It happens from top to bottom in Mexico and is, unfortunately, accepted there.
I know that most companies that do business in Mexico (and other countries where bribery/(large) gift giving is par for the course) have extremely specific policies on dealing with this. I know that mine does.