(CN) – Journalism advocacy groups on Friday filed an ethics complaint against Greg Gianforte, a Republican who reportedly body-slammed a reporter the night before winning a U.S. House special election in Montana.

Press groups PEN America, the Society for Professional Journalists, Free Press and Reporters Without Borders lodged a formal complaint with the Office of Congressional Ethics over Gianforte’s alleged assault of Ben Jacobs, a reporter with The Guardian.

Montana’s special election was required because Ryan Zinke, R-Mont., had resigned his U.S. House seat in March to become President Donald Trump’s Interior Secretary. The night before the election, Gianforte reportedly attacked Jacobs when the reporter attempted to ask Gianforte a question about Trump’s health care plan.

Jacobs recorded the incident and immediately contacted police. Gianforte was charged with misdemeanor assault that night, but went on to win the May 25 election. He has until June 6 to appear on the misdemeanor assault charges in Bozeman municipal court.

Gianforte faces a maximum of 6 months in jail and a $500 fine if convicted. The Gallatin county attorney is also reviewing the case to see if additional charges are merited.

The press groups filed their complaint with the Office of Congressional Ethics, an independent agency within Congress. The office handles ethics complaints from the public and may refer them to a House Committee on Ethics for investigation.

The press freedom groups also wrote to the House Ethics Committee regarding its obligation to open an investigation within 30 days of any House member being charged with a crime, or to file a report to the full House explaining why it has not done so.

Trump also received a letter from the press groups, expressing concern that the White House’s denigration of the media is inciting physical violence against reporters.

Soon after Gianforte was charged with assault, his campaign released a statement saying Jacobs was to blame for the altercation. That claim was contradicted by witness reports and Jacobs’ recording.

Gianforte did not respond to requests for statements the night of the alleged assault, but released an apology after the election results showed him the obvious winner.

“Tonight we won a victory for all Montanans,” Gianforte said in his statement. “Tonight Montanans sent a wakeup call to the Washington D.C. establishment. Montanans said Bernie Sanders and Nancy Pelosi can’t call the shots in Montana. Montanans said we need to drain the swamp.

“And we have a lot of work to do. Hard work is the way we get things done and sometimes hard work is born out of hard lessons.

“Last night I learned a lesson. When you make a mistake, you have to own up to it. That’s the Montana way. Last night I did make a mistake. I took an action that I cannot take back. I am not proud of what happened. I should not have responded the way that I did. And for that I am sorry. I should not have treated the reporter that way. I am sorry Mr. Ben Jacobs… I want to apologize to the FOX News team, and I am sorry to each of you for my actions.

“That is not the person I am or the leader I will be for Montana.”

Within a day of the alleged assault, emails soliciting contributions to pay down campaign debt were sent out from the Gianforte campaign office.

Campaign spokesman Shane Scanlon said the assault occurred when Gianforte was in a private office preparing for an interview with Fox News when Jacobs came in without permission.

According to Jacobs’ recording of the interview, which was posted on The Guardian’s website, Gianforte can be heard yelling at Jacobs, followed by crashing sounds. Jacobs can be heard saying his glasses were broken and he wanted to call the police.

“I’m sick and tired of you guys,” a voice identified as Gianforte’s says in the recording. “The last guy who came in here you did the same thing. Get the hell out of here. Get the hell out of here.”

The press groups said this type of incident is becoming too common in American political coverage.

“It is now clear that the steady stream of criticism of the press from the president and members of his administration – including the president’s notorious claim that they are the ‘enemy of the people’ – is emboldening attacks on reporters and the important work they do,” Suzanne Nossel, executive director of PEN America, said. “The Trump administration’s constant demonization of the media is having a dangerous trickle-down effect. It’s time for the president to be presidential, and defend our free press. If he refuses to speak out, President Trump is complicit in political violence.”

According to the press groups, the Gianforte assault is one of several acts of physical aggression against news media in the last month. On May 9 in West Virginia, a reporter was arrested for asking Health and Human Services Secretary Tom Price a question, and on May 18 in Washington, security guards pinned a reporter for CQ Roll Call against a wall and ejected him under threat of force when he asked a Federal Communications Commission commissioner a question, according to PEN America.

“It is appalling that the hostile anti-press rhetoric being used at various levels of the U.S. government has now escalated to physical violence against a journalist who simply asked a question,” Margaux Ewen of Reporters Without Borders said. “This new level of violence is completely unacceptable in a country founded on democratic values like a free and independent press.”

Gianforte defeated Democrat Rob Quist 190,502 to 169,203. Libertarian Mark Wicks received 21,683 votes. Gianforte had held a slim, double-digit lead going into election day, and that margin was trimmed even further after the attack – giving Democrats a glimmer of hope of regaining the Montana House seat, which a Democrat has not held since 1991.

A wealthy businessman from New Jersey, Gianforte ran for Montana’s only House seat against Quist, a singer/songwriter making his first entrance into politics.

Gianforte had lost the Montana gubernatorial election in November to Democrat Steve Bullock. Gianforte will face another election test in 18 months, in the primary election for his House seat.