Teamsters President Sean O’Brien got into a heated argument with Sen. Markwayne Mullin (R-Okla.) during a Wednesday Senate Health, Education, Labor and Pensions Committee hearing on union busting tactics.   

O’Brien told Mullin he was “out of line” after the GOP senator said that the union leader was “sucking the paycheck” out of workers to earn his salary, which was roughly $193,000 in 2019. 

“Don’t tell me I’m out of line,” Mullin responded. “You need to shut your mouth.” 

Mullin, who owned non-union plumbing companies before selling his majority stakes in 2021, accused union leaders of engaging in intimidation tactics in an effort to unionize his company so they could pay themselves “exorbitant” salaries. 

“We hold greedy CEOs like yourself accountable,” O’Brien responded. “You want to attack my salary, I’ll attack yours. What did you make when you owned your company?”

Mullin—who had a net worth ranging between $31.6 million and $75.6 million in 2020, according to personal financial disclosures analyzed by Oklahoma newspaper Tulsa World—said that he kept his salary to around $50,000 to invest more money into his company.

“You mean you hid money,” O’Brien said, prompting visible outrage from Mullin. 

Mullin finished his remarks by stating that he’s “not anti-union” but believes that workers shouldn’t have to pay union dues if they don’t want to.

In 2013, the Office of Congressional Ethics alleged that then-Rep. Mullin received over $600,000 in outside income from its companies, well above the congressional limit. The House Ethics Committee closed its investigation into Mullin in 2018 and ordered him to repay $40,000 to one of his businesses.

Wednesday’s hearing, hosted by Sen. Bernie Sanders (I-Vt.), the committee’s chairman, focused on anti-union tactics by large companies such as Starbucks, whose CEO Howard Schultz recently agreed to testify before the committee later this month after a subpoena threat from Sanders.