WASHINGTON — Representative Matt Gaetz, an outspoken Florida Republican with close ties to President Trump, has landed in hot water — again.

The bipartisan leaders of the House Ethics Committee said on Friday that Mr. Gaetz had flouted their requests for an in-person interview to answer to accusations that he had “sought to threaten, intimidate, harass or otherwise improperly influence” the congressional testimony of Michael D. Cohen, Mr. Trump’s former personal lawyer and fixer.

Refusing to talk to the committee, which polices the ethical conduct of House members, is exceedingly rare, and the committee leaders said Mr. Gaetz had left them no choice but to form a special investigative subcommittee to look further into the possible threat.

“The committee informed Representative Gaetz that its ability to resolve the complaint would be hindered without his testimony and explained that if the committee was unable to dispose of the complaint by June 24, 2019, House and committee rules would require” the creation of the investigative body, a statement from the Ethics Committee’s top Democrat and Republican said.