Thousands of people in the US city of Milwaukee have protested against plans to criminalise undocumented workers.
Immigrants are said to do many of the jobs Americans do not want to
They oppose a bill passed last year by representatives that would make it a felony to be in the US illegally.
The rally came as President Bush urged Congress to tone down the rhetoric on immigration, which is likely to be a key issue in November's mid-term poll.
Senators are due to debate the issue, with many Republicans opposing Mr Bush's calls for a guest-worker plan.
He is proposing to allow foreigners to remain in the US for a set period of time to carry out specific jobs.
It is estimated that 11.5 million people are living in the US illegally. Many of them work in the agricultural sector and the construction and service industries.
Mr Bush said on Thursday that the message should be: "If you are doing a job that Americans won't do, you're welcome here for a period of time to do that job."
However, his proposals face opposition from some members of his own party - among them Senate Majority Leader Bill Frist - who advocate a tougher line on immigration, including stringent border controls.
Senator Hillary Clinton, a Democrat, has said proposals to criminalise undocumented workers and their support networks "would literally criminalise the Good Samaritan and probably even Jesus himself".
The Senate debate, which is scheduled to begin next week, is expected to last two weeks.
Meanwhile, protests for and against tougher immigration controls are set to continue.
Milwaukee's "Day Without Latinos" protest will be followed by a rally on Saturday in Los Angeles, California, where organisers are hoping to attract 500,000 protesters.
And on Monday, supporters of tighter border controls are planning to take to the streets of Washington and Boston.