If you are a United States citizen and cross the border frequently you may have to pay a fee to go into Mexico.
The National Immigration Institute in Mexico (INAMI) has started a pilot program in which foreigners that enter Mexican territory for more than seven days or they will be involved in paid work, they will have to pay 306 pesos, or about 28 US dollars.
“We are doing what should be done,” said Rudolfo Figueroa, representative of INAMI in Baja California. “Foreigners who enter Mexico have the obligation to register; if they will be in national territory for more than seven days, they have to pay the right of non-residents.”
But we Americans aren't even allowed to keep Mexicans from illegally entering our country or sending them back when they do without being called hateful and racist.