Republican leaders in the US House of Representatives have announced unusual plans to hold hearings around the country on the issue of immigration.
The issue of immigration has proved divisive among Republicans
The move will mean an extended delay to congressional negotiations to agree new legislation on the high-profile issue.
"I'm not putting any timeline on this thing, but I think we need this thing done right," said the House speaker, the Republican Dennis Hastert.
The House and Senate have endorsed very different bills on immigration.
Both seek to tighten border security, but while the Senate bill includes a guest-worker programme and offers illegal immigrants a "path to citizenship", the House bill seeks to deport illegal immigrants and make it a felony to remain in the US illegally.
President George W Bush had hoped negotiations between the two congressional chambers to agree a compromise bill would be wrapped up before mid-term elections in November.
He has endorsed a final bill along the lines of that backed by the Senate.
Analysts say the Republican plans for public hearings are a serious setback for the president. Some paint it as an attempt by conservatives to seize back the political high ground on this hotly contested issue.
There are an estimated 11.5 million illegal immigrants in the United States, and millions of migrants took to the streets in May to protest against stricter measures to keep immigrants out.
Republicans said on Tuesday they would hold field hearings in congressional districts in August in the south, south-west and other areas where the immigration debate is especially fraught.
HOUSE BILL VS SENATE BILL
HOUSE BILL (passed December)
Focuses on border security
Backs construction of fence along border with Mexico
Makes it a felony to live in the US illegally instead of a civil offence
Seeks to deport illegal immigrants
SENATE BILL (passed May)
Also toughens border security
Allows some illegal immigrants to seek US citizenship
Proposes guest-worker programme
Republican aides told the Washington Post likely topics up for debate included claims the Senate plans could allow 100 million new immigrants into the US over the next two decades, and Senate decisions to allow undocumented workers to retain benefits earned while working illegally.
Republican representatives unhappy at the bipartisan bill agreed in the Senate have been emboldened by the victory of Republican Representative Brian Bilbray in a by-election this month in the San Diego area.
Rep Bilbray narrowly defeated his Democrat rival on a platform of opposition to Mr Bush's immigration plans.
"Our number one priority is to secure the border, and right now I haven't heard a lot of pressure to have a path to citizenship," said Mr Hastert.
But some Senate negotiators played down the importance of the hearings.
"There's a general recognition that we need a bill," said Senate Judiciary Committee Chairman Arlen Specter, a Republican senator and key backer of the Senate bill.
"We're going to get together. We're going to sit down and try to work it all out."
White House spokeswoman Dana Perino said President Bush was "undeterred".
"We are committed and we have been working very hard with members [of Congress] to see if we can reach consensus on an issue the American people have said they want action on," she said.