Oklahoma Sen. Markwayne Mullin (R), a former mixed martial arts fighter, nearly came to blows with the president of the Teamsters at a Senate hearing Tuesday, forcing Chair Bernie Sanders (I-Vt.) to step in to stop a brawl from breaking out in the Senate Health, Education, Labor and Pensions Committee room.

Mullin challenged International Brotherhood of Teamsters General President Sean O’Brien to a fight on the spot after the senator read aloud O’Brien’s tweets calling him out as a “clown” and a “fraud.”  

“Sir, this is a time, this is a place. You want to run your mouth, we can be two consenting adults, we can finish it here,” Mullin said from the hearing room dais. 

“OK, that’s fine. Perfect,” O’Brien shot back. 

“You want to do it now?” Mullin asked. “Stand your butt up then.” 

“You stand your butt up,” O’Brien retorted, prompting Mullin, who is 46 years old, to stand up from his chair as if he was preparing to spring into the middle of the hearing room to trade blows with the Teamster.

At that point, Sanders tried to take control of the hearing to stop an impromptu cage match from breaking out.

“Hold it. No, no, no, sit down. Sit down! You’re a United State senator, sit down,” Sanders yelled while banging the gavel to restore order in the room.

“This is a hearing. God knows the American people have enough contempt for Congress, let’s not —” Sanders fumed before being cut off by more bellicose cross-talk between Mullin and O’Brien.  

Mullin then tried to challenge the Teamsters official to a real cage match with the proceeds going to charity, but Sanders gabbed the mic to interrupt his Republican colleague.  

“Excuse me, hold it. Sen. Mullin, I have the mic. If you have questions on any economic issues, anything that was said, go for it. We’re not here to talk about physical abuse,” Sanders said.  

The purpose of the hearing, which was called for by Sanders, was show how unions are improving the lives of working families.

Mullin argued that he was trying to expose O’Brien as a “thug” after the Teamsters leader tweeted at him after a prior contentious Health, Education and Labor Committee hearing in March, when O’Brien called Mullin, who previously owned a plumbing company, a “greedy CEO,” and Mullin told the union official to “shut his mouth.”

The Oklahoma senator didn’t back down or apologize when later asked about his conduct.  

“He called me out. … He said anytime, anyplace. You don’t call me out and say ‘anytime, anyplace,’ and then not back it up what you said,” Mullin said. 

“I answered his call. Period,” he added.  

Asked if he should be held to a higher standard as a member of the U.S. Senate, Mullin said: “I’m still a guy. He called me. He said it. I just answered the bell. That was all.”  

At the hearing, the Oklahoma senator held out printouts of O’Brien’s posts on Twitter, which has been rebranded as X.

“You tweeted at me, one, two, three, four, five times,” Mullin said at the hearing. “Let me read what the last one said: ‘Greedy CEO who pretends like he’s self-made. What a clown, fraud. Always has been, always will be. Quit the tough-guy act in these Senate hearings. You know where to find me, anyplace, anytime.'”

The senator insisted he spent long hours in his plumbing truck building his business, while his wife managed the office.

O’Brien didn’t back down from his tweets, either, calling Mullin “an embarrassment” and telling him to “grow up.”

“You want to fight me? Let’s have coffee, discuss our differences,” he said.  

Updated at 1:10 p.m. ET