Many Hispanic groups urged their members to forgo work, school and shopping on Monday to demonstrate illegal immigrants' economic and political power.

"We have to make our presence felt through our absence," organizers from the nation's most influential Hispanic groups said Friday at their final press conference before the mass boycott.

But Republican Representative Tom Tancredo, chairman of the House Immigration Reform Caucus, said that a day without illegal aliens would be "a boon to the American taxpayer," who wouldnt pay for the tremendous social service costs of persons living in the country illegally.

He said the net cost to the federal government of public services provided to illegal aliens in 2005 was estimated to be 11.7 billion dollars, or 3,080 dollars per each American household.

Monday is a normal work day in the United States, where Labor Day is celebrated in September instead of May 1. However, it might look more like a May Day abroad, complete with demonstrations called by labor unions and workers' rights advocates.

The demonstration was planned by a network representing some 40 million Hispanics.

"We've unequivocally called on all families to participate in the Great American Boycott and the marches -- and that translates into not going to work, not going to school, not shopping and not selling," Nativo Lopez, president of the Mexican-American Political Association, said.

However, city and school officials and the "We Are America" coalition, which includes the Roman Catholic Church, are encouraging people to go to school and work and then join the demonstrations later in the day.

The division over the way the protests should be carried out is as evident among political leaders as it is among unions.