"I want to say publicly what I've said privately to Michael Cohen and to his family, that I'm sorry," he said at the time.
"It's entirely appropriate to test the truthfulness of a witness, but that could've been done in a way that didn't invoke someone's family, and I shouldn't have done it."
In comments to MacCallum Friday, on the lawmaker claimed there has been "no finding that I've done anything wrong."
"I stand by the comments I made on your show. But it really highlights the double standard that exists with today's left."
Gaetz pointed to two Democratic lawmakers whom he claimed made fiery remarks in the past that didn't lead to a congressional probe.
"We've got members of Congress -- Maxine Waters actually incited violence against Republicans and supporters of the president," he claimed.
"We had Rashida Tlaib ... using profanity to talk about how she was going to impeach the president.
"I guess when a Republican says something that might go a little over the line," he said, "it might be treated a little differently."
The Florida lawmaker added he believed there are better things for the Democrat-led House to focus on.
"I'm worried about the 5,500 people that show up at our border every day," he said. "I worry about the fact that we haven't changed our asylum laws," he added, calling on House Speaker Nancy Pelosi to hold a vote on the USMCA trade deal with Mexico and Canada.
MacCallum pressed Gaetz on the tweet, and whether he was "threatening a witness the night before he was about to testify."
She pointed to bipartisan criticism at the time from Sen. Rick Scott, R-Fla., and Rep. Adam Schiff, D-Calif.
Gaetz responded, considering whether his support for President Trump played a factor in the committee's decision.
"There very well may be a coordinated effort to go after people like me, people like Kellyanne Conway, who are effective advocates for a transformational president," he said, referring to the White House counselor who's been accused of violating the Hatch Act.
Gaetz has since deleted the original tweet directed at Cohen, in which he wrote: “Do your wife & father-in-law know about your girlfriends? Maybe tonight would be a good time for that chat. I wonder if she’ll remain faithful when you’re in prison. She’s about to learn a lot...”
The tweet was sent on the eve of testimony from Cohen, Trump's former attorney, on Capitol Hill.
In a statement Friday, House Ethics Committee Chairman Ted Deutch, D-Fla., and ranking member Kenny Marchant, R-Texas, said they'd established a subcommittee to review the incident.
"On March 13, 2019, the committee received a member complaint against Rep. Matt Gaetz," the statement read. "The committee then began a review ... into allegations that Representative Gaetz sought to threaten, intimidate, harass or otherwise improperly influence the president’s former attorney, Michael Cohen, in connection with Mr. Cohen’s testimony before a congressional committee."
In May, Gaetz declined a request to appear for an in-person interview, according to the committee's statement.
The subcommittee will be chaired by Rep. Anthony Brown, D-Md., with Rep. Michael Guest, R-Miss., serving as ranking member.
"The committee notes that the mere fact of establishing an investigative subcommittee does not itself indicate that any violation has occurred," the statement read.
Fox News' Elizabeth Zwirz and Stephen Sorace contributed to this report.