CNN host Jake Tapper confronted the union leader who was challenged by Republican Sen. Markwayne Mullin of Oklahoma to a fight during a Tuesday hearing.

Mullin and Teamsters Union boss Sean O’Brien had a heated exchange during the hearing held by the Senate Committee on Health, Education, Labor and Pensions, with the Oklahoma senator getting up from his chair before Independent Sen. Bernard Sanders of Vermont restored order. Mullin is a former professional mixed martial arts (MMA) fighter who went undefeated, according to his official Senate web page. (RELATED: Teachers Union Boss Claims Antisemitism, Homophobia ‘Rolled Into’ Attacks On Her)

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“What went through my mind was ‘You’re one of 100 of the most powerful people in the country and you’re acting like a 12-year-old in a schoolyard because you didn’t get your way,’” O’Brien told Tapper. “I mean, look, he actually has the ability, and he’s one of the elite, to actually effectuate change in this country, and he’s focused on being a bully.”

“Ok. But can I say, you’re tweeting like a 12-year-old?” Tapper responded.

Mullin and O’Brien also exchanged trash talk in June after the union leader labeled the senator a “greedy CEO.” Mullin, who left college to keep a family plumbing business afloat according to his Senate bio, extended an offer to meet O’Brien in a MMA octagon in a charity match via a June 26 post on Twitter.

“I mean, we had some great dialog in there about issues that affect working people, about organizing collective bargaining, unionizing America and there was a lot of different opinions, a lot of different debate,” O’Brien claimed. “And it was great until Markwayne Mullin, obviously we were renting space in his head, decided to erupt.”

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