Lawmakers return to the US Congress on Saturday with no clear path to resolving a squabble that appears likely to close wide swaths of the federal government, from national parks to financial regulation, in less than 18 hours.

Infighting among Republicans who control the House of Representatives has pushed the United States to the brink of its fourth partial shutdown in a decade, as the chamber has been unable to pass legislation that would keep the government open beyond the October 1 start of the fiscal year.

On the other side of the Capitol, the Democratic-controlled Senate is due to advance a stopgap funding bill, but a final vote might not come for days.

Hundreds of thousands of federal employees will lack the funding to do their jobs if the two chambers do not send a spending bill for Democratic President Joe Biden to sign into law by 12:01 a.m. (0401 GMT) on Sunday.

Federal agencies have already drawn up detailed plans that spell out what services must continue, like airport screening and border patrols, and what must shut down, like scientific research and nutrition aid to 7 million poor mothers.

Most of the government’s 4 million-plus employees would not get paid, whether they were working or not.

In Atlanta, festivities for former president Jimmy Carter’s 99th birthday were moved up from Sunday to Saturday to avoid disruption, according to local media.

The standoff comes just months after Congress brought the federal government to the brink of defaulting on its $31.4 trillion debt. The drama has raised worries on Wall Street, where the Moody’s ratings agency has warned it could damage US creditworthiness.

Congress typically passes stopgap spending bills to buy more time to negotiate the detailed legislation that sets funding for federal programmes.

This year, a group of Republicans has blocked action in the House as they have pressed to tighten immigration and cut spending below levels agreed to in the debt-ceiling standoff last spring.

On Friday, 21 Republicans joined with Democrats to defeat legislation that reflected those demands, saying the chamber should focus instead on passing detailed spending bills for the full fiscal year, even if it leads to a shutdown in the near term.

That angered other Republicans, who said they had blown an opportunity to advance conservative policies.

“There’s a lot of frustration growing with the 21 individuals who chose to vote ‘no’ on what was a very good plan,” Republican Representative Nicole Malliotakis of New York said on Friday.

House Speaker Kevin McCarthy said the chamber might try to rely on Democrats to help pass a stopgap bill that would continue funding at current levels, even though that could prompt a challenge to his leadership from hardliners. He did not provide further details.

The Senate is due to hold a procedural vote at 1:00 p.m. (1700 GMT) to extend government funding through Nov. 17. It enjoys wide support from Republicans and Democrats, but the chamber’s numerous hurdles mean that a vote on final passage could be delayed until Tuesday.

Even if that passes, the two chambers would have to resolve their differences before sending any bill to Biden’s desk. That could pose another hurdle, as McCarthy said he opposed $6 billion in Ukraine aid included in the Senate bill.

“We continue to try to find a way out of this,” he said on Friday.