Thousands of demonstrators gather in downtown Los Angeles to take part in an immigration protest on Monday, May 1, 2006. [AP]

From Los Angeles to Chicago, Houston to Miami, the "Day Without Immigrants" attracted widespread participation despite divisions among activists over whether a boycott would send the right message to Washington lawmakers considering sweeping immigration reform.

"We are the backbone of what America is, legal or illegal, it doesn't matter," said Melanie Lugo, who with her husband and their third-grade daughter joined a rally of some 75,000 in Denver. "We butter each other's bread. They need us as much as we need them."

Two major rallies in Los Angeles attracted an estimated 400,000, according to the mayor's office. Police in Chicago estimated 400,000 people marched through the downtown business district.

Tens of thousands more marched in New York, along with about 15,000 in Houston, 50,000 in San Jose and 30,000 more across Florida. Smaller rallies in cities from Pennsylvania and Connecticut to Arizona and South Dakota attracted hundreds not thousands.

In all, police departments in more than two dozen U.S. cities contacted by The Associated Press gave crowd estimates that totaled about 1.1 million marchers.

The mood was jubilant. Marchers standing shoulder-to-shoulder filmed themselves on home video and families sang and chanted and danced in the streets wearing American flags as capes and bandanas. In most cities, those who rallied wore white to signify peace and solidarity.

In Los Angeles, the city streets were a carpet of undulating white that stretched for several miles, with palm trees and grass-covered medians poking through a sea of humanity. Marchers holding U.S. flags aloft sang the national anthem in English as traditional Mexican dancers wove through the crowd.

In Chicago, illegal immigrants from Ireland and Poland marched alongside Hispanics as office workers on lunch breaks clapped. In Phoenix, protesters formed a human chain in front of Wal-Mart and Home Depot stores. Protesters in Tijuana, Mexico, blocked vehicle traffic heading to San Diego at the world's busiest border crossing.

Many carried signs in Spanish that translated to "We are America" and "Today we march, tomorrow we vote." Others waved Mexican flags or wore hats and scarves from their native countries. Some chanted "USA" while others shouted slogans, such as "Si se puede!" Spanish for "Yes, it can be done!" Others were more irreverent, wearing T-shirts that read "I'm illegal. So what?"

The White House reacted coolly.

"The president is not a fan of boycotts," said press secretary Scott McClellan. "People have the right to peacefully express their views, but the president wants to see comprehensive reform pass the Congress so that he can sign it into law."

The boycott was organized by immigrant activists angered by federal legislation that would criminalize illegal immigrants and fortify the U.S-Mexico border. Its goal was to raise awareness about immigrants' economic power.

Industries that rely on immigrant workers were clearly affected, though the impact was not uniform.

Tyson Foods Inc., the world's largest meat producer, shuttered about a dozen of its more than 100 plants and saw "higher-than-usual absenteeism" at others. Most of the closures were in states such as Iowa and Nebraska. Eight of 14 Perdue Farms chicken plants also closed for the day.

Goya Foods, which bills itself as the nation's largest Hispanic-owned food chain, suspended delivery everywhere except Florida, saying it wanted to express solidarity with immigrants who are its primary customers.

None of the 175 seasonal laborers who normally work Mike Collins' 500 acres of Vidalia onion fields in southeastern Georgia showed up.

"We need to be going wide open this time of year to get these onions out of the field," he said. "We've got orders to fill. Losing a day in this part of the season causes a tremendous amount of problems."

It was the same story in Indiana, where the owner of a landscaping business said he was at a loss. About 25 Hispanic workers ¡ª 90 percent of the field work force ¡ª never reported Monday to Salsbery Brothers Landscaping.

"We're basically shut down in our busiest month of the year," said owner Jeff Salsbery. "It's going to cost me thousands of dollars."

In the Los Angeles area, restaurants and markets were dark and truckers avoided the nation's largest shipping port. About one in three small businesses was closed downtown, including the cluttered produce market and fashion district.

The construction and nursery industries were among the hardest hit by the work stoppage in Florida.

Bill Spann, executive vice president of the Associated General Contractors of Greater Florida said more than half the workers at construction sites in Miami-Dade County did not show up Monday.

"If I lose my job, it's worth it," said Jose Cruz, an immigrant from El Salvador who protested with several thousand others in the rural Florida city of Homestead rather than work his construction job. "It's worth losing several jobs to get my papers."

But the effect was minimal in some places. On Manhattan's busy 14th Street, only a few shops were closed, including a Spanish-language bookstore and a tiny Latin American restaurant.

The impact on some school systems was significant. In the sprawling Los Angeles Unified School District, which is 73 percent Hispanic, about 72,000 middle and high school students were absent ¡ª roughly one in every four.

In San Francisco, Benita Olmedo pulled her 11-year-old daughter and 7-year-old son from school.

"I want my children to know their mother is not a criminal," said Olmedo, a nanny who came here illegally in 1986 from Mexico. "I want them to be as strong I am. This shows our strength."

Truck traffic at the twin ports of Los Angeles and Long Beach ¡ª the nation's largest port complex ¡ª was off 90 percent, said spokeswoman Theresa Adams Lopez.

Some of the rallies drew small numbers of counter-protesters, including one in Pensacola, Fla.

"You should send all of the 13 million aliens home, then you take all of the welfare recipients who are taking a free check and make them do those jobs," said Jack Culberson, a retired Army colonel who attended the Pensacola rally. "It's as simple as that."

Jesse Hernandez, who owns a Birmingham, Ala., company that supplies Hispanic laborers to companies around the Southeast, shut down his four-person office in solidarity with the demonstrations.

"Unfortunately," he said, "human nature is that you don't really know what you have until you don't have it."