Article 32 of the Constitution of Mexico --
Only Mexicans by birth can perform all government employments, positions, or commissions in which the status of citizenship is indispensable.
During peacetime, foreigners shall neither serve in the Army nor in the police bodies. During peacetime, only Mexicans by birth can serve in the Army, in the Navy or in the Air Force as well can perform any employment or commission within such corporations.
The same condition applies to captains, pilots, skippers, ship engineers, flight engineers and, in general, to every crew member in a ship or an airplane carrying the Mexican flag. In the same way, only Mexicans by birth can be port harbormasters, steersmen and airport superintendents.
Mexicans shall have priority over foreigners, under equal circumstances, for all kind of concessions, employments, positions or commissions of the government in which the status of citizenship is not indispensable.