WASHINGTON (AP) - A bipartisan group of US senators plans to unveil proposed legislation on Tuesday that would represent the most dramatic changes to the country's immigration system in two decades.
The senators already are defending the programme that would provide a pathway to citizenship for the 11 million individuals in the country who came illegally or overstayed their visit.
"We're not awarding anybody anything. All we're doing is giving people the opportunity to eventually earn access to our new, improved and modernised legal immigration system," said Senator Marco Rubio, a Republican and potential presidential candidate in 2016 who has been at work on the deal.
Immigration represents a rare issue on which President Barack Obama's fellow Democrats and opposition Republicans might actually reach agreement.
The Republicans were jolted into a major reassessment after losing badly in last year's elections - and losing the Hispanic vote - and have been looking for ways to reach beyond their largely ageing white male image.
The measure would put millions who are in the US illegally on a 13-year path to citizenship, while toughening border security requirements, mandating that all employers check the legal status of workers and allowing tens of thousands of new high- and low-skilled workers into the country with new visa programs.
The legislation is expected to include a new emphasis on merit-based immigration over family ties.
Senator Rubio had been slow to fully embrace the proposal. But he promoted the pending legislation on Sunday talk shows, leaving little doubt he was going to work to win over skeptics.
"What we're working on is a starting point. It is not the take-it-or-leave-it offer. It is a starting point of reform," Mr Rubio said.
But even before its release, the proposal has its critics. Republican lawmakers are mindful that the party's base still favours a tough stance on illegal immigration.
"I'm not convinced," said Senator Jeff Sessions, a Republican from Alabama, which has pursued one of the strictest approaches to illegal immigration in recent years.
"They have produced legislation ... that will give amnesty now, legalise everyone that's here effectively today and then there's a promise of enforcement in the future."
Senator Mike Lee, a Republican, said he could consider supporting the proposal only if the first priority were border security. Senator Rubio insisted it is. "If you are undocumented here now, if you are illegally in the US, then you can't even apply for this until these plans are in place and they begin to implement them," he said.
"And then you're going to have to pay a fine. You're going to have to pay an application fee. You're going to have to pass a background check."
Other lawmakers helping to write the legislation acknowledged the political challenges of the issue.
"A lot of my conservative colleagues have significant questions, and they're legitimate," said Senator John McCain, a Republican from Arizona, which shares a border with Mexico.
"This is the start of a process ... I am guardedly optimistic that we will see finally the end of this long, long trek that a lot of us have been on for many years."