The US Justice Department launched a grand jury investigation into allegations that the head of the United Auto Workers pressured another high-ranking union official to secure benefits for his fiancée and her sister, according to internal communications within the labor organization.

A federal grand jury has subpoenaed the union’s court-appointed monitor as it probes the claims against President Shawn Fain, according to emails seen by Bloomberg News. The messages were sent to Fain, UAW Vice President Rich Boyer and members of the law firm representing the union.

Fain called the allegations “false” in a statement to Bloomberg and accused Boyer, whose complaints to the monitor drew early scrutiny to union leadership, of trying to influence the upcoming UAW election. Boyer didn’t respond to multiple requests for comment about Fain’s accusations against him.

Steven Fagell, an attorney with Covington & Burling, which represents the union, said in an email that the UAW broadly is not the subject of a grand jury investigation. The DOJ didn’t immediately respond to a request for comment outside of regular business hours. A representative for the monitor declined comment.

While probes by federal prosecutors can end without any charges being brought, the DOJ’s action intensifies pressure on the scandal-plagued union, which resolved a long-running corruption probein 2020 when it agreed to the appointment of the monitor to keep watch over the UAW’s governance. That prior investigation, conducted before Fain was elected, uncovered corruption in the upper ranks, including embezzlement of union funds and other efforts to cover up misuse of cash that sent two past union presidents and other UAW leaders to prison.