The head of one of the state’s largest and most politically influential public employee unions has resigned amid an investigation into unspecified allegations, according to a brief statement from the union Thursday.

John Westmoreland had been on leave as executive director of Council 5 of the American Federation of State, County and Municipal Employees — known as AFSCME — since the union’s board ordered an outside investigation of him in August.

The union, which has more than 43,000 members, has not disclosed any information about the nature of the allegation nor the outcome of the investigation. It was led by an “outside entity,” according to an earlier statement from the union.

“The Council, all of its members and the employees we represent are grateful for the many years of commitment and sacrifice that John gave to this organization in service of the workers throughout the state of Minnesota,” read the statement from the union.

Westmoreland could not be reached for comment.

AFSCME’s executive board named Julie Bleyhl, the union’s senior Capitol lobbyist, as interim executive director. The statement said Westmoreland resigned Wednesday.

Bleyhl did not respond to e-mail or phone messages.

The shake-up comes on the heels of a successful negotiation between AFSCME and the administration of Gov. Tim Walz for a new contract, which will give state workers raises of 2.25% this year and 2.5% next year, with modest increases in employee health care contributions and a generous student loan repayment plan.

The contract still has to be approved by a legislative subcommittee.

AFSCME members perform a wide range of government jobs, from state prison guards to county child protection workers.

AFSCME poured hundreds of thousands of dollars into the 2018 election, fearing a Republican takeover of both the Legislature and the executive branch, which would likely mean an effort to undercut the collective-bargaining rights and political influence of the union.

Janus v. AFSCME, a 2018 U.S. Supreme Court decision, was a major blow to the union, preventing collection of dues from nonmembers even when those workers received the benefits of collective-bargaining agreements.

In the face of the legal and political environment, AFSCME Council 5 helped elect both Walz and a DFL-majority Minnesota House, giving them key political allies.

Westmoreland ascended to the union’s top job in November 2017 after the retirement of longtime AFSCME leader Eliot Seide. Westmoreland had previously been Council 5’s assistant director and had also held other AFSCME positions. He became involved in the union while working as a prison guard in Stillwater.