A hardline Republican says he will seek to oust House Speaker Kevin McCarthy this week, after he pushed through a last-minute spending bill with support from the opposition Democrats.
Mr McCarthy submitted the bill – aimed at averting a government shutdown – in defiance of the right of his party.
They had already vowed to topple him if he tried to overcome their opposition with Democratic support.
Hardline Republicans in both houses of Congress voted against the motion.
Republicans control the House of Representatives, with Democrats enjoying a wafer-thin majority in the Senate.
On Sunday, Rep Matt Gaetz vowed to oust Mr McCarthy, telling the CNN that House Republicans needed “trustworthy” leadership.
“I do intend to file a motion to vacate against Speaker McCarthy this week,” said Mr Gaetz, long a vocal critic of the Californian congressman. “I think we need to move on with new leadership that can be trustworthy.”
The Florida Congressman, who is among the party’s most right-wing members and a keen ally of former President Donald Trump, has been threatening to force a vote on Mr McCarthy’s future for weeks.
Along with other hard-right Republicans in the so-called Freedom Caucus, Mr Gaetz refused to back successive budgets proposed by Mr McCarthy, insisting on heavy spending cuts and an end to new military aid to Ukraine.
The hard-right faction said any attempt to pass a spending bill by relying on Democratic votes would cross a red-line which would prompt an attempt to remove the Speaker from his leadership position.
But in a dramatic turnaround on Saturday afternoon, Mr McCarthy decided to put to a vote the temporary funding measure that would keep the government open until 17 November. It contains funding for natural disasters but makes no major concessions on spending levels – a key demand of the Republicans controlling the lower house.
Mr McCarthy admitted that the last-minute agreement was not the route he wanted to take, telling reporters that he had “tried to pass the most conservative stopgap measure possible,” but “we didn’t have 218 Republicans”.
Mr Gaetz has long been a thorn in Mr McCarthy’s side. In January, he repeatedly refused to back him in the Speaker’s race, resulting in a record 15 rounds of voting.
He eventually relented after securing a number of concession, including a rule change allowing just one member to file a so-called motion to vacate – a move to remove the Speaker – which he is now threatening to use against Mr McCarthy.
“Speaker McCarthy made an agreement with House conservatives in January, and since then he has been in brazen, repeated material breach of that agreement,” Mr Gaetz said on Sunday. “This agreement that he made with Democrats, to really blow past a lot of the spending guardrails we had set up, is a last straw.”
But speaking on CBS on Sunday, Mr McCarthy sought to dismiss Mr Gaetz’s challenge, calling his criticism “personal”.
“I’ll survive,” Mr McCarthy said. “He’s more interested in securing TV interviews.”
“Let’s get over with it. Let’s start governing. If he’s upset because he tried to push us into a shutdown and I made sure government didn’t shut down, then let’s have that talk,” he added.