Outgoing US President Donald Trump has set up an uncomfortable test of Republican allegiances, by threatening to stall Congress’s massive COVID relief package, unless it includes bigger cheques for Americans.

House Democrats who also favour $US2000 cheques will all but dare Republicans to break with Mr Trump on Thursday, calling up his proposal for a Christmas Eve vote.

The President’s last-minute objection could derail critical legislation amid a raging pandemic and deep economic uncertainty.

His attacks also risk a federal government shutdown by early next week.

Mr. President, sign the bill to keep government open! Urge McConnell and McCarthy to agree with the Democratic unanimous consent request for $2,000 direct payments! This can be done by noon on Christmas Eve!

— Nancy Pelosi (@SpeakerPelosi) December 23, 2020

“Just when you think you have seen it all,” House Speaker Nancy Pelosi wrote in a letter to colleagues.

“The entire country knows that it is urgent for the President to sign this bill, both to provide the coronavirus relief and to keep government open.”

Republicans led by Senate Majority Leader Mitch McConnell have previously resisted $2000 cheques as too costly.

House Republicans are expected to block the vote, but Democrats may try again on Monday.

The President’s push to increase direct payments for most Americans from $600 to $2000 for individuals and $4000 for couples splits the party with a politically painful loyalty test, including for GOP senators David Perdue and Kelly Loeffler, who are fighting to retain their seats in the January 5 special election in Georgia.

ATTN GA: COVID-19 relief is on the way!

Nearly $1 trillion will be distributed to help Georgians & those across the country who need it the most.

This has been an extremely difficult year for many, and this new round of aid is designed to support hardworking Americans. pic.twitter.com/ma46JsQzCO

— Senator Kelly Loeffler (@SenatorLoeffler) December 22, 2020

On a conference call, House Republican lawmakers complained that Mr Trump threw them under the bus, according to one source. Most had voted for the package and they urged leaders to hit the cable news shows to explain its benefits, the person said.

The relief bill Mr Trump is criticising would establish a temporary $300 per week supplemental jobless benefit, along with a new round of subsidies for hard-hit businesses, restaurants and theatres and money for schools, health care providers and renters facing eviction.

Even though Treasury Secretary Steven Mnuchin represented the White House in negotiations, Mr Trump assailed the bipartisan effort in a video he tweeted out Tuesday night, suggesting he may not sign the legislation.

Railing against a range of provisions in the broader government funding package, including foreign aid mainstays included each year, Trump called the bill a “disgrace.”

The final text of the more than 5000-page bill was still being prepared by Congress and was not expected to be sent to the White House for Mr Trump’s signature before Thursday or Friday, an aide said.

A resolution could be forced on Monday. That’s when a stopgap funding bill Congress approved to keep the government funded while the paperwork was being compiled expires, risking a federal shutdown.

The House was already set to return Monday, and the Senate Tuesday, for a vote to override Trump’s veto of the must-pass defence bill.

Democrats may try again at that time to pass Mr Trump’s proposal for $2000 cheques, as well as the temporary government funding measure to avert a shutdown, the aides said.

Republicans have been reluctant to spend more on pandemic relief and only agreed to the big year-end package as time dwindled for a final deal.

Senator Chuck Schumer, the Senate Democratic leader, said that “Trump needs to sign the bill to help people and keep the government open,” and Congress would step up for more aid after.

The Senate cleared the huge relief package by a 92-6 vote after the House approved it by 359-53. Those votes totals would be enough to override a veto should Mr Trump decide to take that step.

President-elect Joe Biden applauded lawmakers for their work.

He described the package as far from perfect, “but it does provide vital relief at a critical time”.

-AAP