They are kept that way by the constitution, which separates police officers from other public servants, meaning they do not qualify for the standard minimum wage and the 40-hour weekly work limit.

ECONOMIST: Organised crime in Mexico

In more detail, Don Boudreaux runs through the standard objections to a minimum wage.

FORBES: Greg Mankiw's Excellent Question: Why a $9 Minimum Wage? Why Not $90? Or 90 cents?