U.S. lobbyists lashed out Wednesday at the Mexican ''Nothing Gringo'' campaign timed for Monday to coincide with the ''Day Without Immigrants'' boycott in the United States.

The American Chamber of Commerce in Mexico said organizers are risking a backlash and foolishly targeting some of their best allies, since U.S. corporations have actively lobbied the U.S. Congress for immigration reform including legalization for many of the estimated 11 million undocumented migrants.

Mexicans' refusal to ''buy American'' on Monday could further polarize the debate and make reform supporters seem anti-American at the very moment that lobbyists are trying to persuade lawmakers in Washington to pass a bill that would benefit migrants, worries Larry Rubin, the chamber's president.

Migrants and their supporters in the United States are being encouraged to skip work and school and not spend money for one day to demonstrate the migrants' importance to the U.S. economy.

South of the border, Mexicans are targeting American stores and chain restaurants -- 'That means no Dunkin' Donuts, no McDonald's, Burger King, Starbucks, Sears, Krispy Kreme or Wal-Mart,'' reads one e-mail making the rounds.

But even activists are confused about which companies are U.S.-owned. Sears is cited by boycott organizers, despite the fact that Sears' Mexico stores were bought by Mexican billionaire Carlos Slim in 1997. And few organizers mention Vips -- the chain of ubiquitous Mexican diners -- even though they are owned by Wal-Mart Stores.

A quarter of Mexico's formal private-sector jobs with regular pay are provided by U.S. firms, according to the chamber, including Walmex, the Mexican Wal-Mart subsidiary that is the nation's biggest private employer with 140,000 workers. Delphi, the U.S. auto parts maker, is second with 70,000 workers.

The chamber represents more than 2,000 American and other foreign companies doing business in Mexico and says its members are responsible for $100 billion of investment in the country.

The companies say they're helping Mexico by providing jobs, but activists counter they pay so little that Mexicans have little choice but to head north.

Backers of the Mexican boycott insisted Wednesday that the protest could send a message that American companies should offer better pay and benefits to their Mexican workers.

Unskilled workers at U.S. companies usually start with Mexico's minimum wage of $4.35 a day. While many earn more, such as seamstresses making an average of $5.89 a day -- even these wages pale in comparison to paychecks offered by the same companies north of the border, conceded the chamber's Humberto Banuelos.

''Yes, we are aware that they are the largest employers in the Mexican republic, but they are paying crumbs,'' said Martha Suarez Cantu, coordinator of Alianza Braceroproa, a Mexican labor-rights group helping organize the boycott.

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