Shawn Fain, the president of United Auto Workers, is under investigation by an independent federal monitor over allegations of retaliation against other union leaders, according to a court filing on Monday.

Neil Barofsky, the union’s monitor, opened an investigation in February to review allegations, including one from the UAW secretary-treasurer, Margaret Mock, saying she had faced retaliation for her refusal or reluctance to authorize certain expenditures for Fain’s office, according to the filing. Barofsky also opened a probe into Mock’s actions.

Fain said in a statement that he encouraged the monitor “to investigate whatever claims are brought to their office, because we know what they’ll find: a UAW leadership committed to serving the membership, and running a democratic union”.

Fain added: “Taking our union in a new direction means sometimes you have to rock the boat, and that upsets some people who want to keep the status quo.”

Barofsky was appointed federal monitor in 2021 as the UAW grappled with a corruption scandal that resulted in the federal convictions of several former leaders. Two former UAW presidents were sentenced to prison time as part of the probe.

The monitor expanded his investigation to also include allegations made by Fain against the leader of the union’s Stellantis department, Rich Boyer. Fain took over Boyer’s duties at the end of May.

Union officials did not immediately respond to requests for comment on behalf of Boyer and Mock.

Fain alleged Boyer’s responsibilities were reassigned because of his “dereliction of duty” in connection with collective bargaining issues.

The monitor later received complaints that Fain’s decision was an act of retaliation because Boyer refused to engage in acts of financial misconduct to benefit others, according to the court filing.

The monitor said the union had not produced the documents he requested quickly enough. UAW officials have turned over approximately 2,600 documents of the potentially relevant pool of about 116,000 documents, according to the filing.

The Department of Justice also informed the monitor that the union’s position was “making it difficult, if not impossible, for the Monitor to fulfill his mandate to remove fraud, corruption and illegality from within the UAW”, the filing said.

Fain assumed his post last year after narrowly winning the first direct election in the union’s history. He led the labor group through a six-week strike against Detroit automakers last autumn, and is spearheading a nationwide organizing campaign across the US south and west.

That campaign suffered a blow last month when the union lost a vote at a Mercedes plant in Alabama. Weeks earlier, it had clinched a historic victory at a Volkswagen plant in Tennessee.

Fain has emerged as an important figure for Joe Biden during this election year as the president tries to win over autoworkers and voters in Michigan, a key swing state.

Biden joined Fain at a picket line in Michigan to support striking autoworkers in September. Fain also attended the 2024 State of the Union address, after the UAW endorsed Biden in January.