Hundreds of Mexican union members took to the streets of central Mexico City early Monday to support Mexican migrants living and working in the United States and to boycott U.S. goods in what was dubbed a "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 here — an action timed to coincide with a call for immigrants to boycott work, school and shopping in the United States.

But measuring the impact of the actions was likely to prove difficult: Business already is normally reduced to a fraction of normal volume on Mexico's May Day holiday.

Marina Serna, deputy manager for Burger King in downtown Mexico City, said she thought it had an effect: The restaurant had only one client in its first 90 minutes open on Monday, even though it is owned by Mexican franchise holders.

"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," she said.

CountryWatch: Mexico

But there was a steady stream of customers at one Wal-Mart "Super Center" in Mexico City.

Juan Ortiz, a 28-year-old salesman who left the store pushing a cartload of food and bathroom goods, said he supported legalizing migrants in the U.S., but didn't think it was practical to boycott U.S. goods here.

"You have to buy what is least expensive here and I have to buy things for my family," he said.

Celestino Garcia, a 32-year-old sandwich seller outside the Wal-mart, said he was seeing the same number of shoppers entering and leaving the store Monday as on any other day.

At the U.S. Embassy on Mexico City's central Paseo de la Reforma boulevard, about 50 police officers, many of them carrying helmets, batons and plastic shields, took up position behind 15-foot (4.5-meter) barricades as supporters of the Zapatista rebel movement prepared to welcome their leader, Subcomandante Marcos, who has spoken out in favor of the boycott and U.S. work stoppages.

One supporter wore the group's traditional black mask and a T-shirt bearing a likeness of Cuban revolutionary icon Che Guevara, as well as Nike Air Jordan pants and Converse sneakers.

Federal officials have tried to distance themselves from both the U.S. and Mexican protests, and President Vicente Fox on Sunday urged Mexicans who plan to participate in the protests to be prudent.

"They shouldn't be an element of provocation or one that promotes xenophobia or opposition" to immigration reform, Fox said.

Fox said he is convinced U.S. lawmakers are likely to pass legislation benefiting the millions of undocumented Mexican migrants living and working north of the border.

"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."

Fox has called repeatedly since taking office in 2000 for a migration accord.

He has also criticized a bill passed by the U.S. House of Representatives in December that called for construction of 1,100 kilometers (700 miles) of fence along the 3,220-kilometer (2,000 mile) U.S.-Mexican border, calling the proposal "stupid."

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."