By WILL WEISSERT Associated Press Writer MEXICO CITY Hundreds of union members rallied Monday to support Mexican migrants working in the United States and call for a boycott of U.S. goods in what was dubbed "A Day Without Gringos." The boycott call by unions came as Mexico celebrated May Day, a holiday dedicated to workers and when business is a fraction of the normal. Immigration rallies also are planned across the United States, where immigrants are being urged to boycott work, school and shopping as part of the "Day Without Immigrants." At least a half-dozen state governors in Mexico endorsed the boycott of McDonald's, Wal-Mart and hundreds of other U.S. companies here. Measuring the impact of the actions was likely to prove difficult. Marina Serna, deputy manager for Burger King in downtown Mexico City, said she believed it had an effect. The restaurant had only one client during the first 90 minutes it was open, even though it is owned by Mexicans. "I'd say that this is bad because even if we work in a company with an international brand, the owners are not from the United States, they are Mexicans," Serna said. Mexico's restive union movement _ which traditionally holds rallies on May 1 _ dedicated this year's march to the legalization of undocumented workers in the United States. Federal officials have tried to distance themselves from protests in both nations. President Vicente Fox on Sunday urged Mexican protesters to be prudent. "They shouldn't be an element of provocation or one that promotes xenophobia or opposition" to immigration reform, Fox said. Monday's marches were expected to pass in front of the U.S. Embassy on the capital's stylish Paseo de la Reforma Boulevard, where Zapatista leader Subcomandante Marcos also planned a rally in favor of the boycott in the United States. Fox said he was convinced legislation benefiting undocumented Mexican migrants living and working north of the border likely would be passed by U.S. lawmakers soon. "They know the importance and value of immigration for the United States and they also know that it's a topic that can benefit both countries," Fox said. "It's a topic that brings us closer together and that allows us to understand each other better." Since taking office in 2000, Fox repeatedly has called for a migration accord that would legalize the millions of undocumented Mexican workers living in the United States. He also has criticized as "stupid" a U.S. House of Representatives bill calling for the construction of 700 miles of fence along the 1,952-mile U.S.-Mexican border. However, his administration has held back from getting involved in the protests, saying it does not want to violate U.S. sovereignty. The president also said his government must "generate opportunities here in Mexico." "And then, if someone wants to leave, to conquer new horizons, they should go ahead and do it," Fox said, "but only after there are opportunities in Mexico."