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

Monitor Neil Barofsky opened an investigation in February to review allegations, including that theUAWsecretary treasurer said 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 the secretary treasurer’s actions.

TheUAWdeclined to comment.

Barofsky was appointed the federal monitor in 2021 as theUAWgrappled with a corruption scandal that resulted in the federal convictions of several former leaders.

Two formerUAWpresidents 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. Fain took over the Stellantis department leader’s duties at the end of May.

Fain alleged that the Stellantis department head’s responsibilities were reassigned because of their “dereliction of duty” in connection with collective bargaining issues.

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

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

The Department of Justice also informed the monitor that the “Unions position is 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 unions history. He led the labor group through a six-week strike against the Detroit automakers last autumn, and is spearheading a nationwide organizing campaign across the 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 President Bidenduring this election year as the US leader tries to win over auto workers and Michigan voters.

Biden joined Fain ata picket line in Michigan to support striking auto workers in September. Fain also attended the 2024 State of the Union Address, after theUAWendorsed Biden in January.