Walking into Mexico at the nation’s busiest border crossing with the United States is no longer an uninterrupted stroll for foreigners.

Starting late Wednesday, pedestrians going to Tijuana from San Diego at the San Ysidro crossing must choose between a line for Mexicans who get waved through, and a line for foreigners who must show a passport, fill out a form and—if staying more than a week—pay 322 pesos, or roughly $20, for a six-month permit.