The measure, which also tightens border security and workplace enforcement measures, unites a group of influential liberals, centrists and conservatives and has White House backing, but it has drawn criticism from across the political spectrum. In a nod to that opposition, Senate leaders won't seek to complete it before a hoped-for Memorial Day deadline.
"It would be to the best interests of the Senate ... that we not try to finish this bill this week," said Senate Majority Leader Harry Reid, D-Nev., as the chamber began debate on the volatile issue. "I think we could, but I'm afraid the conclusion wouldn't be anything that anyone wanted."
The immigration bill, hailed as a bipartisan breakthrough last week, began to be picked apart this week, first by Senate Republicans, reports CBS News chief White House correspondent Jim Axelrod.
Republicans want to make the bill tougher on the nation's estimated 12 million illegal immigrants. Democrats want to change a new temporary worker program and reorder priorities in a merit-based system for future immigration that weights employability over family ties.
The unlikely coalition that brokered the deal, led by Sens. Edward M. Kennedy, D-Mass., and Jon Kyl, R-Ariz., is keeping an eye on the legislation to guard against "deal-breaker" changes that would sap its support. The group will hold daily meetings starting Tuesday to determine whether proposed revisions would sink what they are calling their "grand bargain."
"We have to try our very best to work together to get something that will actually pass," Kyl said.
Among the first changes to be debated will be a proposal by Sen. Jeff Bingaman, D-N.M., to shrink the temporary worker program created by the compromise plan. Some lawmakers in both parties consider the initiative, which would provide at least 400,000 guest worker visas annually, too large.
Others charge it's impractical and unfair to immigrants, because it would allow them to stay only temporarily in the U.S. without guaranteeing them a chance to gain legal status.
"We must not create a law that guarantees a permanent underclass, people who are here to work in low-wage, low-skilled jobs but do not have the chance to put down roots or benefit from the opportunities of American citizenship," Reid said.
Reid called the measure a "starting point," but said he had reservations about it.
The measure calls for tougher border security and changes the entry criteria, emphasizing employability over family ties, adds Axelrod. But undocumented workers already here could get visas to stay while they seek permanent residency. That's what critics call "amnesty," a deal breaker for many conservatives.