Mr Obama's stimulus plan is set for debate in Congress this week
Prominent Republicans have threatened to vote against US President Barack Obama's $825bn economic stimulus plan.
Senator John McCain called for tax cuts rather than increased spending, while House minority leader John Boehner said the package needs substantial changes.
The Republicans do not have enough votes to defeat the package, but they could delay it in the senate.
Speaker Nancy Pelosi has promised to bring the stimulus package to a vote in the House of Representatives this week.
At the same time, the senate will begin drawing up another version that is likely to give Republicans more of what they want, the BBC's Sarah Morris reports from Washington.
She says it all adds up to a huge early test of President Obama's ability to fix the economy with large bi-partisan majorities.
Speaking to Fox television, Mr McCain said the package does not do enough to create jobs.
"There have to be major rewrites if we want to stimulate the economy," he said. "As it stands now, I can't vote for it."
Mr Boehner also criticised the plan: "I just think there's a lot of slow-moving government spending in this program that won't work... We can't borrow and spend our way back to prosperity."
Hoping to change their minds, Mr Obama will hold private meetings with the Republican leadership on Tuesday.
His proposed plan will send the American budget deficit above $2 trillion amid the worst economic crisis in decades.
US Vice President Joe Biden, who spent the weekend trying to persuade Republican senators to come to a compromise, had earlier sounded an optimistic note.
"I think we'll get a significant bipartisan support out of the Senate," he said.