WASHINGTON, March 26: Against a background of rising political tension and public protests, the US Senate begins a crucial debate on Monday on a law that seeks to criminalise undocumented immigrants. More than 500,000 people participated in a huge protest rally in downtown Los Angeles this weekend to show their resentment against a proposed law that would make it a felony to be in the US illegally.

The House of Representatives has already passed the law which now goes to the upper house, the Senate. “This could be a fractious debate, and I hope it’s not,” warned President Bush who has proposed an alternative guest workers programme that would allow people to work in the US for a specific period but will not qualify them for green cards or US citizenship.

Since Thursday hundreds of thousands of people have joined in rallies in cities including Milwaukee, Los Angeles, Phoenix and Atlanta, and staged school walkouts, marches and work stoppages.

The demonstrations are expected to culminate on April 10 in a “National Day of Action” organized by labour, immigration, civil rights and religious groups.

This weekend’s protests surprised even the organizers who acknowledge that they did not expect such huge turnouts. Even in Denver, a city of half a million people, more than 50,000 came out to protest.

In Phoenix, an estimated 20,000 people gathered for one of the biggest demonstrations in the city’s history. The proposed law would impose new penalties on employers who hire illegal immigrants, require churches to check the legal status of parishioners before helping them and erect fences along one-third of the US-Mexican border.

“As we debate the immigration issue, we must remember there are hardworking individuals, doing jobs that Americans will not do, who are contributing to the economic vitality of our country,” said President Bush.