Republican Senator Markwayne Mullin of Oklahoma and Teamsters President Sean O'Brien were on the verge of a physical altercation during a Senate committee hearing on Tuesday. The tense confrontation occurred during a Health, Education, Labor and Pensions Committee hearing, where O'Brien was appearing as a witness.

The clash began when Mullin referenced a heated exchange between the two during a previous hearing in March. Mullin brought up a series of tweets in which O'Brien had called him names such as a "greedy CEO," a "clown," and a "fraud." Mullin then read one of O'Brien's tweets aloud, in which O'Brien challenged him to a fight, saying, "You know where to find me. Any time, any place, cowboy."

In response, Mullin pointed to the floor between the dais and the witness table and said, "This is a place." O'Brien, seemingly unfazed, replied, "Okay, that's fine. I'd love to do it right now." Mullin then stood up and dared O'Brien to do the same. O'Brien retorted, "You stand your butt up, big guy."

As the situation escalated, Senate committee chairman Bernie Sanders, attempting to maintain order, implored them to stop. "You're a United States senator," Sanders reminded Mullin. However, both Mullin and O'Brien persisted in their argument, disregarding Sanders' pleas.

The exchange between the two continued for several minutes, with Mullin accusing O'Brien of being “quiet” in the face of a challenge, and O'Brien criticizing Mullin's behavior. Mullin then pointed a finger at O'Brien and called him a "thug," prompting O'Brien to label Mullin as "disrespectful." Sanders repeatedly banged his gavel and tried to regain control of the situation, emphasizing that the hearing was meant to discuss economic issues, not physical altercations.

Despite Sanders' efforts, Mullin and O'Brien continued to bicker until the hearing moved on to the next line of questioning from other committee members. The contentious history between the two dates back to their previous clash in March, where Sanders also had to intervene. The ongoing animosity between them was evident as they disregarded Sanders' calls for calm and spoke over each other.

Mullin, who is a former undefeated Mixed Martial Arts (MMA) fighter, has a reputation for his fighting prowess, having a professional record of 5-0. O'Brien is the president of the International Brotherhood of Teamsters, one of the nation's largest and most influential unions.

Fox News Digital reached out to the offices of Mullin and Sanders, as well as the Teamsters, for comment but did not receive an immediate response. The confrontation between Mullin and O'Brien adds to the already tense atmosphere in Congress, following a separate physical altercation involving lawmakers on Capitol Hill.

In that incident, GOP Representative Tim Burchett accused former House Speaker Kevin McCarthy of elbowing him in the back during a meeting of House Republicans, leading Burchett to chase after McCarthy.

The clash between Mullin and O'Brien highlights the deep divisions and animosity within Congress, as lawmakers engage in heated confrontations over political and personal differences.