The embattled New York Republican congressman George Santos has been accused of sexual harassment by a former aide.

Santos already faces local, state, federal and international investigations over professional and personal behaviour, campaign finance filings and a campaign résumé shown to be largely made-up.

He has admitted embellishing his résumé but denied wrongdoing and said he will not resign, as members of his own party and Democrats have repeatedly urged him to do.

Republican leaders who must govern with a slim House majority have stood by him, though he has withdrawn from two committees.

On Friday, the former aide, Derek Myers, published on Twitter a letter to the House ethics committee in which he claimed to have been put to work in Santos’s office as a volunteer, in violation of ethics rules, and to have been harassed.

“Today,” he wrote, “I filed a police report with Capitol police and a complaint with the House ethics committee regarding ethical violations and sexual harassment by Congressman George Santos during my time working in his office.

Myers added: “These matters will not be litigated on social media or through news media. They are serious offenses and the evidence and facts will speak for themselves if the committee takes up the matter. This tweet is being made public in light of transparency.”

In his letter, Myers wrote that he was “alone with the congressman” in his personal office on 25 January, going over constituents’ mail.

“The congressman earlier in the day had asked me if I had a Grindr profile,” Myers wrote, “which is widely known as an LGBTQ+ social networking app, more commonly used for sexual intercourse”.

Santos told him he had a profile, he said.

In the personal office, Myers alleged, Santos “called me ‘buddy’ and insisted I sit next to him on a small sofa”.

The congressman, Myers said, put a hand on his knee and asked if he wanted to go out to karaoke. Myers said he declined, whereupon Santos moved his hand to Myers’ inner thigh and groin.

Myers alleged Santos said: “My husband is out of town tonight if you want to come over.” Myers said he pushed Santos away and left the office.

Five days later, he wrote, he was asked, as he had been during his hiring process, about his background as a journalist in Ohio, where he faced wiretapping charges after publishing recorded court testimony. The next day, Myers says, he was “informed that my job offer was being rescinded”.

The New York Times reported that a spokesperson for the ranking Democrat on the House ethics committee acknowledged receipt of Myers’ letter. The paper said Capitol police did not confirm receipt of a report.

Santos’s lawyer declined to comment, the paper said.

On Thursday, Santos told Semafor he did not hire Myers because of the Ohio charges. Santos’s chief of staff said the same to Talking Points Memo (TPM), to which Myers gave a recording of the conversation with Santos in which he was let go.

Santos said Myers’ charges in Ohio were “not concerning to us, it’s concerning to this institution”. Myers told TPM that as Santos spoke, he was “thinking to myself, ‘I’m a threat and concern to this institution – George Santos, you’re George Santos!’”