Hundreds of thousands of people in more than 100 cities across the United States were taking part in rallies to mark the biggest of a wave of demonstrations over controversial laws on immigration reform.

The protests are designed to illustrate growing anger among sections of America's Latino population at a proposed crackdown on illegal workers, including the construction of a wall along the entire Mexican border.

Major rallies were being held in in Los Angeles, Phoenix, Chicago, Atlanta, Boston, Washington and Houston. Protestors were gathering in dozens of other towns across the US.

Today's demonstrations follow weeks of debate over how the US should handle the growing flood of illegal immigrants entering the country in search of a share of the American dream.

Although they consume precious resources and are exploited by criminal gangs, the workers also provide the cheap food, goods and services demanded by the middle classes.

Avril Smith, of the Service Employees International Union, one of many groups co-ordinating the day of action, said: "We think this will be the largest mobilisation on the issue of immigration reform ever."

The House of Representatives has passed legislation that would make illegal entry to the US a crime and step up the building of a 700-mile barrier on the US-Mexico border.

Efforts in the Senate to agree a less draconian Bill, which would open the way for undocumented workers to be legalised and make illegal immigration a civil offence rather than a felony, collapsed on Friday, paving the way for continued protests while Congress is in recess for Easter.

Yesterday an estimated 500,000 people took part in a march in Dallas. The demonstrators waved US flags and banners saying "United We Stand. We pray for legal status" or "We are not terrorists".

The Roman Catholic Church has supported the illegal workers and Archbishop John Favalora addressed the crowd before a march through Miami.

Republican Senator Arlen Specter, chairman of the Senate Judiciary Committee, said that he remained optimistic the Senate would pass an acceptable Bill when it returns from its two-week spring recess.

"Everybody agrees there’s an enormous problem, and everybody agrees with the border security lines. There’s general agreement that we have to craft a compromise. There's a real risk of significant political fallout here, and members think about that. I think tempers will cool" he said.

Organisers of today's rallies hope to top the late March protests in 44 US cities, in which they said 1.5 million people took to the streets.

Hispanic voters represent about 12.5 per cent of the US electorate, a proportion which is rising fast and is already higher than that for black people. Karl Rove, the senior strategist to President Bush, identifies these voters as proto-Republicans who usually have socially conservative views despite being left-of-centre on economic issues.

Mr Bush has remained vague on the issue, saying he wanted a Bill that recognised that America had been built by immigrants, while stopping short of an automatic amnesty for illegal workers.

Times Recommends

• No cause for celebration in crushed Sarajevo
• Jazz funeral for the final victims of Katrina
• French fined for 'insulting' civil servants