A revised Republican bill to raise the US debt ceiling, cut spending and avert a federal default is set for a crunch House of Representatives vote later.
But House Speaker John Boehner's bill faces a conservative revolt, unanimous opposition by Senate Democrats and a White House veto threat.
Republicans hold 240 of the 433 votes to be cast, and need 217 of their members to back the bill to pass it.
Mr Boehner told dissenting colleagues on Wednesday: "Get your ass in line."
The US Treasury has warned the government will run out of money to pay all its bills unless a $14.3tn borrowing limit is increased by next Tuesday.
Mr Boehner's plan would trim $917bn from the US budget deficit over 10 years and raise the debt limit by up to $900bn.
President Barack Obama supports another plan by top Senate Democrat Harry Reid, which would cut $2.2tn from deficits, and raise the debt ceiling by $2.7tn.
But that is thought unlikely in its current form to pass the Republican-controlled House.
Both Republican and Democratic plans underwent revisions on Wednesday after congressional budget analysts said the savings advertised by each one had been overstated.
The Boehner and Reid plans overlap in key ways - trimming spending over 10 years, shunning President Obama's call for tax increases on the wealthy and creating special lawmaker committees to craft future cuts.
But Mr Boehner's approach would force another debt-limit showdown during next year's presidential campaign, something Mr Obama has fiercely opposed.
Senate Majority Leader Reid's plan would see the ceiling lifted until after the November 2012 elections.
http://www.bbc.co.uk/news/world-us-canada-14328183
Note: 28 July 2011 Last updated at 14:07 GMT