The 38-year-old is under scrutiny by federal prosecutors over whether he had sex with a 17-year-old and other underage girls and violated federal sex trafficking laws. That's according to people familiar with the investigation who spoke on condition of anonymity because they could not discuss details publicly.
Gaetz, who has not been charged with any crimes, denied the accusations Monday.
"First, I have never, ever paid for sex," he wrote. "And second, I, as an adult man, have not slept with a 17-year-old."
Engaged since New Year's Eve, he wrote, "My lifestyle of yesteryear may be different from how I live now, but it was not and is not illegal."
Gaetz used his column to attack Democrats, news organisations and others, saying his enemies are "just repeating false allegations about a congressman who loathes the swamp and fights both sides of it on a daily basis."
He also predicted, "I'm sure some partisan crooks in Merrick Garland's Justice Department want to pervert the truth and the law to go after me."
The FBI, the Biden administration's Justice Department and "the Cheney political dynasty" were among the entities Gaetz accused of unjustly targeting him.
The Justice Department investigation began last year while Trump was still president. Gaetz helped lead an unsuccessful battle in January to depose Rep. Liz Cheney, R-Wyo., daughter of former Vice President Dick Cheney, from her job as No 3 House GOP leader. Days earlier, she was among just 10 House Republicans to vote to impeach Trump.
Gaetz's article was published the same day a former congressional aide told reporters he was interviewed last week by the FBI. Nathan Nelson, a military adviser who left Gaetz's office in October, said he was questioned about whether he'd left that job because he knew of Gaetz's "involvement in illegal activities".
"I'm here this morning to state that nothing could be farther from the truth. Neither I nor any other member of Congressman Gaetz's staff had any knowledge of illegal activities," Nelson said at his home in Santa Rosa Beach, Florida.
Nelson provided no specific details about the FBI's questioning. Without detailing them, he said he believes the charges against Gaetz are false.