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BS) LOS ANGELES Several thousand participants have already packed the streets of downtown Los Angeles. Organizers expect several hundred thousand people to march from Broadway and Olympic to City Hall in protest to a bill before Congress to strengthen enforcement of immigration laws.

Critics are protesting a bill introduced by Rep. F. James Sensenbrenner, R-Wis. Would crack down on employers who hire illegal workers as well as “coyotes” that smuggle illegal immigrants into the country.

HR 4437 would require employers to verify Social Security numbers with the Department of Homeland Security, increase penalties for immigrant smuggling and for undocumented workers who return to the U.S. after being sent back to their native country.

Local law enforcement would benefit, as they would be reimbursed for detaining illegal immigrants. Refugees with aggravated felony convictions would be denied green cards.

Protest organizer Javier Rodriguez believed undocumented immigrants are essential to America’s labor force and should not be criminalized.

"We will not accept less on the immigration reform than the pass to legalization for the 12 million undocumented immigrants that are in this country," Rodriguez said.

"If the politicians do not keep the public opinion of the American public, a majority of Americans want legalization for the undocumented population, then we will then move on a national level toward a national economic boycott," Rodriguez said.

On the other hand, L.A. County Supervisor Mike Antonovich was sympathetic towards the legislation.

"I feel it deals effectively with the catastrophic effects illegal immigration have had on the county," Antonovich said. "It provides the necessary penalities and reforms that are now lacking and which have created a magnet for illegals to enter our country."

Thousands of students walked out of school and hit the streets from Huntington Park, South Gate, Montebello, Jordan, Garfield, Roosevelt, Washington Preparatory and Bell High schools Friday to protest the bill.

The group will advocate for "the need for immigration reform that respects the dignity of every human being in the U.S. and therefore (we are) calling for the legalization of the undocumented who are here," said Alvaro Huerta, of the Coalition for Humane Immigration Rights of Los Angeles.

Activists from the United Farm Workers union are scheduled to hold rallies Sunday morning at the Federal Building and the Cathedral of Our Lady of the Angels.

(© 2006 CBS Broadcasting Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)