US President-elect Donald Trump urged Republican lawmakers Wednesday to scupper a cross-party deal to avert a fast-looming US government shutdown.

Staring down a Friday night deadline to fund federal agencies, party leaders in Congress had agreed on a "continuing resolution" (CR) to keep the lights on until mid-March and avoid having to send public workers home without pay over Christmas.

But the compromise was pilloried by numerous Republicans - most notably tech billionaire Elon Musk, whom Trump has charged with slashing government spending in his second term.

The Tesla and SpaceX CEO has emerged as a major voice in US politics and took to his X platform with a flurry of posts - many of them inaccurate - denouncing extra spending in the text that ballooned costs.

Trump holds huge sway over Republicans and his intervention makes it almost certain that the bill will fail.

Suggesting that concessions to Democrats in the text were "a betrayal of our country," Trump called in a joint statement with Vice President-elect J.D. Vance for Republicans to "GET SMART and TOUGH."

Trump and Vance said they would be against any package that does not include an extension to the federal borrowing limit, which the country is on track to hit just as Republicans take total control of Congress in January.

The current federal debt is $36.2 trillion and Congress has raised the limit more than 100 times to allow the government to meet its spending commitments. The next extension was not part of the shutdown negotiations and the demand took lawmakers by surprise.

The bill includes more than $100 billion in disaster relief requested by the White House, $30 billion in aid for farmers, restrictions on investment in China and the first pay raise for lawmakers since 2009.

But the add-ons to the package sparked a rebellion in Republican ranks, meaning the leadership would have been forced to lean on Democratic votes - a tactic that got the previous House speaker, Kevin McCarthy, axed by his own side.

"House Republicans have been ordered to shut down the government. And hurt the working class Americans they claim to support. You break the bipartisan agreement, you own the consequences that follow," said Democratic House Minority Leader Hakeem Jeffries.

The stakes of the negotiations are particularly high for McCarthy's replacement, Mike Johnson, whose bid to retain the House speaker's gavel in a January vote looks imperiled given a firestorm of criticism over the legislation.

'Outrageous spending'

A CR is required because neither chamber had been able to agree on the various departmental budgets for the full 2025 fiscal year, which started on October 1.

Government departments and services, from national parks to border control, will begin shuttering Saturday unless an agreement is reached.

Dozens of Republicans in the House - where they have a razor-thin majority and can only lose three members in partisan votes - look set to oppose the bill if it survives Trump's intervention.

Rank-and-file Republicans typically object to temporary funding agreements because they keep spending levels static rather than introducing cuts and are invariably stuffed with "pork" - extra spending shoehorned in without proper debate.

Before Trump spoke out, Musk had sent more than two dozen posts attacking the text.

"This bill should not pass," he said in one message, before posting a photo of all 1,547 pages piled up, and asking: "Ever seen a bigger piece of pork?"

He also said it was "criminal" to include funding for a State Department program countering foreign propaganda, which he dismissed as a "censorship operation."

And he said any lawmaker voting for the "outrageous spending bill deserves to be voted out in 2 years!"

Musk has no expertise or experience in government funding and many of his claims were wide of the mark including that a shutdown would not harm the country and that the pay raise for lawmakers would be 40 percent. The real figure is less than four percent.

He also amplified false claims that the bill was paying for a new football stadium in Washington and that it would fund "bioweapon labs."

A five-week shutdown from 2018 to 2019 shrank the economy by about $3 billion, according to the Congressional Budget Office.