Representative Matt Gaetz of Florida moved on Monday to oust Speaker Kevin McCarthy from his post in an act of vengeance that posed the clearest threat yet to Mr. McCarthy’s tenure and could plunge the House into chaos.

After days of warnings, Mr. Gaetz rose on Monday evening to bring up a resolution declaring the speakership vacant. That started a process that would force a vote within days on whether to keep Mr. McCarthy in his post. In doing so, Mr. Gaetz sought to subject Mr. McCarthy to a rare form of political punishment experienced by only two other speakers in the 234-year history of the House of Representatives.

The move came just days after Mr. McCarthy opted to avert a government shutdown the only way he could — by relying on Democratic votes to push through a stopgap spending bill over the objections of an unmovable bloc of hard-liners in his own party, including Mr. Gaetz.

It was a brief but tense interruption of the day-to-day proceedings of the House. Mr. McCarthy was not present on the House floor when Mr. Gaetz made his motion, but scores of Democrats crowded in the aisles to watch the spectacle. The House adjourned shortly afterward, but under the chamber’s rules, Mr. McCarthy and his leadership team will need to address it within two legislative days.

“It is becoming increasingly clear who the speaker of the House already works for, and it’s not the Republican conference,” Mr. Gaetz said earlier Monday, making the case for Mr. McCarthy’s ouster. He added that the speaker had allowed President Biden to take his “lunch money in every negotiation.”

Mr. Gaetz cited Mr. McCarthy’s dependence on Democrats to pass the funding bill — which was necessary to avert a shutdown because Mr. Gaetz and 20 of his colleagues opposed a temporary funding bill. And he accused Mr. McCarthy of lying to his Republican members during spending negotiations and making a “secret deal” with Democrats about funding for Ukraine, which he and dozens of other conservatives have opposed.

The move is a significant escalation of the long-simmering power struggle between Mr. McCarthy and a clutch of conservative hard-liners in his party. They have dangled the threat of dethroning the speaker since he was elected, after they subjected him to a painful round of 15 votes.

Mr. McCarthy, a chronic optimist who has shown a remarkable willingness to weather political pain to maintain his grip on the speaker’s gavel, appeared undaunted. Minutes after Mr. Gaetz filed the resolution, he wrote on social media, “Bring it on.”

“I think it’s disruptive to the country, and my focus is only on getting our work done,” Mr. McCarthy said earlier Monday. “I want to win the vote so I can finish the job for the American people. There are certain people who have done this since the day we came in.”

Mr. Gaetz’s animus toward Mr. McCarthy extends far beyond the most recent funding skirmish. He emerged as Mr. McCarthy’s chief tormentor during the speaker’s fight in January, when he suggested on the House floor that the California Republican had “sold shares of himself for more than a decade,” and never quite stopped.

It was to appease Mr. Gaetz and the 19 other Republicans who opposed his speakership that Mr. McCarthy agreed to change the rules of the House to allow any one lawmaker to call a snap vote for his ouster.

After Mr. McCarthy struck a bipartisan deal with Mr. Biden in the spring to suspend the debt ceiling, there were rumblings among the far right about moving forward on a motion to vacate. They settled for shutting down the House floor instead.

It was unclear how many Republicans planned to join Mr. Gaetz in his attempt to dethrone Mr. McCarthy. Some archconservatives who have been critical of the speaker have said in recent days that they would not support removing him now.

But Mr. Gaetz told reporters at the Capitol he had sufficient G.OP. backing to prevail — unless Democrats voted to save Mr. McCarthy.

“I have enough Republicans,” he said. Four other Republicans, Representatives Tim Burchett of Tennessee, Eli Crane and Andy Biggs of Arizona, and Bob Good of Virginia, have said they were inclined to support the motion. More have signaled openness to it.

It remained to be seen whether Democrats would help Mr. McCarthy maintain his post. If they were to vote against Mr. McCarthy — as is almost always the case when a speaker of the opposing party is being elected — Mr. Gaetz would need only a handful of Republicans to join the opposition to remove him, which requires a simple majority vote.

But Mr. McCarthy could hang onto his gavel if enough Democrats voted to support him, skipped the vote altogether or voted “present.” In that situation, Democrats who did not register a vote would lower the threshold for a majority and make it easier to defeat Mr. Gaetz’s motion.

Some Democrats representing moderate and conservative-leaning districts have indicated that they would be hard-pressed to punish Mr. McCarthy for working across the aisle to prevent a shutdown.

But others said they saw no reason to bail him out, pointing to the string of concessions Mr. McCarthy has made to appease his right flank. Those included opening an impeachment inquiry into Mr. Biden and reneging on spending levels negotiated with the president during the debt limit crisis.

In a statement, Representative Ilhan Omar, Democrat of Minnesota, savaged Mr. McCarthy for his opposition to abortion rights and measures to combat climate change. She called him “a weak speaker who has routinely put his self-interest over his constituents, the American people and the Constitution.”

Mr. McCarthy “has made it his mission to cover up a criminal conspiracy from Donald Trump, and is himself a threat to our democracy,” she said. “He literally voted to overturn the 2020 election results, overthrow the duly elected president and did nothing to discourage his members from doing the same.”

Mr. Gaetz’s antics have infuriated Mr. McCarthy’s allies, who view the Florida Republican’s campaign as a publicity stunt motivated by personal animus. As Mr. Gaetz waited to speak on the House floor on Monday, Representative Tom McClintock, Republican of California, rose and chastised him to his face without naming him. Mr. McClintock said he could not “conceive of a more counterproductive and self-destructive course” than to try to remove the speaker from one’s own party.

“I implore my Republican colleagues to look past their prejudices, their passions, their errors of opinion, their local interests and their selfish views,” Mr. McClintock said.

Even some Republicans who initially opposed Mr. McCarthy’s speakership indicated on Monday that they would not back Mr. Gaetz’s drive to dethrone him. Representative Chip Roy of Texas, an influential conservative, said on “The Sean Hannity Show” that he believed “the speaker deserves the ability to finish this year’s process.”

But he hinted that he would be open to getting rid of Mr. McCarthy if the speaker moved to approve aid to Ukraine without also securing the southern border.

“The gloves are off then,” Mr. Roy said.

There are a number of procedural sleights of hand that Mr. McCarthy and his allies could use to try to avoid an up-or-down vote on whether to keep him as speaker. He could hold a vote to table the resolution, which would effectively kill it, or refer it to a committee made up of his allies.

Still, Mr. Gaetz’s decision pushes the House into rarely tested waters.

Only two other speakers have faced motions to vacate: once in 1910, and more recently, in 2015, when Representative Mark Meadows, Republican of North Carolina, sought to oust Speaker John A. Boehner. The House never voted on the motion, but it contributed to Mr. Boehner’s decision to give up his gavel and resign from Congress.

Luke Broadwater and Karoun Demirjian contributed reporting.