Immigrant advocates, Hispanic organizations and refugee-aid groups say they are alarmed at a Republican bill that is heading for a House vote as soon as Thursday.

They say the bill would send asylum seekers back to their persecutors and would broaden the definition of human smuggling and harboring to include religious and humanitarian groups that help immigrants with basic needs.

The bill prohibits people from providing any transport that might aid a person's "illegal entry into or illegal presence in the United States."

Cecilia Munoz, vice president for policy at the National Council of La Raza, a Hispanic civil rights group, said that if the measure became law, a church group that found a man dying of dehydration in the desert and took him to the hospital could be liable for harboring an illegal immigrant and subject to criminal penalties.

"We are doing everything in our power to let people know that this is a huge mistake," said Marshall Fitz, advocacy director for the American Immigration Lawyers Association. "This is an extraordinary change in the way we have treated people in this country."

The measure -- sponsored by Rep. James Sensenbrenner, R-Wis., chairman of the House Judiciary Committee -- would increase penalties for employers that hire illegal immigrants, stiffen sentences for human smugglers and make illegal presence in the United States a felony.

It also would require employers to verify the legal status of their workers and would authorize a process through which sheriffs in 29 counties along the country's southern border could enforce federal immigration laws.

Proponents say it will help bring order to a porous border and stop the flow of illegal immigrants. The lack of border security, they say, poses a national security threat because terrorists can sneak people or weapons into the United States. There are an estimated 11 million illegal immigrants in the United States.

"This legislation will help restore the integrity of our nation's borders and re-establish respect for our laws by holding violators accountable, including human traffickers, employers who hire illegal aliens and alien gang members who terrorize communities throughout the country," Sensenbrenner said in a statement.

The bill does not include President Bush's plan for a temporary worker program that would let millions of illegal immigrants apply for short-term work visas.

The U.S. Chamber of Commerce has criticized the bill for that reason. And Republican lawmakers are split on offering work visas to illegal immigrants.

The Senate, which will address the issue in January, is expected to include a temporary worker plan in its bill, leading to a showdown with the House.

Hispanic groups say that changing the law to make illegal presence in the United States a felony instead of a civil offense would turn all illegal immigrants -- including nearly 2 million children -- into aggravated felons.

Fitz said the bill would severely punish people for many minor immigration violations -- such as a legal resident who forgets to notify the government of a change of address or a foreign student who drops a class and is no longer carrying a full 12-hour course load.

If violators were prosecuted under the new law, they could be subject to a year in prison and lose their chance of ever becoming naturalized citizens, he said.

Immigrant and refugee advocates also said the legislation would limit review of decisions to grant asylum, eroding the due process rights of immigrants.

"The bill basically stacks the deck against refugees," said Eleanor Acer, director of the refugee protection program of Human Rights First. "It also undermines this country's long tradition of providing refuge to those who flee oppression."

The measure isn't nearly stringent enough for some conservatives, who are pushing plans that would radically alter U.S. relations with illegal immigrants.

Rep. Duncan Hunter, R-Calif., chairman of the House Armed Services Committee, plans to offer an amendment to build fences at strategic locations on the U.S.-Mexico border.

Other proposals include discounting noncitizens during the Census and denying citizenship to illegal immigrants' U.S.-born children, McClatchy newspapers reported.

"Now is the time for bold steps, not incrementalism," Arizona Republican J.D. Hayworth said.