MEXICO CITY - Thousands of union members rallied Monday to support Mexican migrants working in the United States and call for a boycott of American goods in what was dubbed “A Day Without Gringos.”

At least a half-dozen state governors in Mexico endorsed the boycott of McDonald’s, Wal-Mart and hundreds of other U.S. companies — an action timed to coincide with a call for immigrants to boycott work, school and shopping in the United States to show their importance to the country.

Measuring the impact of the boycott in Mexico was likely to prove difficult: Business normally drops to a fraction of its ordinary volume on May Day, the international workers’ holiday.