Obama: Congress can finish immigration reform by autumn
US President Barack Obama has called on Congress to pass immigration reform by the end of summer, as the legislation cleared a major procedural hurdle.
If lawmakers were "serious" about fixing immigration, "this is the vehicle to do it," Mr Obama said.
At the legislation's core is a 13-year path to citizenship for immigrants who came to the US illegally.
Hispanic voters' growing political clout has encouraged many in Congress to take up immigration reform.
"There's no reason Congress can't get this done by the end of the summer," said Mr Obama, who won an overwhelming majority of the Hispanic vote in November's election but who before Tuesday had largely stayed out of the public negotiations over the bill.
"There's no good reason to play procedural games or engage in obstruction just to block the best chance we've had in years to address this problem in a way that's fair to middle class families, business owners and legal immigrants."
On Tuesday afternoon, the Senate voted to begin debate on the immigration overhaul bill by a large majority, 82-15.
Senators will now consider a series of amendments with an aim to take a final vote before the 4 July recess.
Aside from the path to citizenship, which would begin with a provisional status open to the estimated 11 million people living in the country illegally, the legislation also creates new or expanded visa programmes for high-skilled and agricultural workers.
The bill enjoys bipartisan support, gaining another Republican backer on Sunday when New Hampshire Senator Kelly Ayotte told CBS News it was a "thoughtful bipartisan solution to a tough problem".
But several Republican senators have called for significant changes, including stricter border control measures beyond what is in the current bill.
"In days ahead there will be major changes in this bill if it is to become law," said Mitch McConnell, the top Republican in the Senate.
The legislation includes $6bn (£3.8bn) in border control funds and aims for a goal of 100% surveillance of the US-Mexico border, with 90% of illegal crossers turned back.
Republican Senator John Cornyn of Texas has proposed an amendment that would require those goals to be met as well as the establishment of additional border security measures, including a biometric exit system, before any immigrant with provisional status can become a permanent resident.
But Harry Reid, the leader of the Senate's Democratic majority, has said Mr Cornyn's amendment is a "poison pill" intended to kill the bill.
And one of the bill's authors, Republican Marco Rubio, suggested the bill should tighten English language proficiency requirements for immigrants.
Correspondents say many Republicans acknowledge the need to overhaul the immigration system given that Hispanics - an increasingly key voter bloc and a significant percentage of US immigrants - overwhelmingly chose Mr Obama, a Democrat, in November's presidential election.
Halting child deportations
Supporters hope the Senate bill will pass with significant bipartisan support in order to move the Republican-led House of Representatives to action.
House Speaker John Boehner, a Republican, said he expected immigration reform to be law by the end of the year, but said the border security measures in the Senate bill were insufficient.
"I believe that it's important for the House to work its will on this issue," Mr Boehner told ABC News.
Last week, House Republicans passed a measure to resume deportations of immigrant children brought to the US illegally by their parents.
Mr Obama created a programme last year to suspend such deportations, and the measure is not expected to be taken up by the Senate.
Representative Chris Van Hollen, a leading House Democrat, has told broadcaster CNBC he believed Mr Boehner wanted to pass immigration reform but was unsure what was feasible in the Republican-controlled House, where conservatives dominate.
"The question is whether or not his caucus is willing to support that effort," Mr Van Hollen said.