ST. PAUL (AP) — Human Services Commissioner Tony Lourey resigned abruptly Monday as head of Minnesota’s largest state agency, just days after his two deputy commissioners quit with no public explanation.

Lourey said in a resignation letter to Gov. Tim Walz that the Department of Human Services needs new leadership to “best execute” the governor’s vision, but didn’t otherwise explain why he was stepping down just six months into a job some lawmakers call one of the toughest posts in state government.

Walz gave few specifics on why Lourey was leaving, but said he didn’t seek his resignation. He credited the Democratic former state senator with using his knowledge to shepherd the agency’s budget through the legislative session and prevent the expiration of a disputed tax on health care providers that provides critical funding for health programs.

“He believes now is the time to put someone with a different skill set in to manage the agency post-budget,” Walz said at a news conference.

Walz said former state finance commissioner Pam Wheelock will step in Tuesday as acting commissioner.

The department consumes nearly one-third of state spending, or about $13.3 billion in the current two-year budget, and serves about 1 million of the state’s vulnerable residents, including the elderly, the poor, the disabled, the mentally ill and children. Only schools get a bigger share of the state’s budget.

Lourey last week announced that Deputy Commissioners Chuck Johnson and Claire Wilson would leave the agency in the next few weeks but didn’t say why. The governor said he didn’t know if the two deputies might stay now and deferred to Wheelock, but said the two had spoken with his chief of staff and that neither was packing up their offices Monday.

Lourey was not giving interviews Monday, spokewoman Katie Bauer said.

Human Services has long been under fire for its handling of alleged fraud , data breaches and other administrative problems. Another blow came in recent days when it emerged that DHS Inspector General Carolyn Ham — placed on leave in March after a critical audit over the agency’s tracking of fraud in child care — had collected $42,000 on paid leave while still waiting for an investigation into her performance to begin. That investigation just began, officials said.

Republican legislative leaders said at a separate news conference that Lourey’s resignation may have been warranted, but they weren’t satisfied with the Democratic governor’s explanations amid the turmoil at the agency.

“Frankly, it’s too early in the Walz administration to have a scandal of this size. So it’s time that the Walz administration is transparent and honest with Minnesotans about what is going on at DHS,” House Minority Leader Kurt Daudt said.

Sen. Michelle Benson, who chairs a committee that oversees the department’s budget, said the agency may be “too big of an entrenched bureaucracy even for somebody with Tony Lourey’s experience to transform.” She called on Walz to bring in private sector experts to take a “radical look” at the agency’s structure and culture.

Two key Democrats on human services issues who know the department well from their work said they had no inside information on Lourey’s resignation but agreed that managing such a large agency would be difficult for anyone.

“This is the hardest job in state government and I don’t know how anybody knows if they’re able to do it until they try,” said Rep. Tina Liebling, who chairs the House committee that oversees the department’s budget. She added that Lourey had a great skill set when it came to negotiating the department’s budget, “but at the end maybe he didn’t have the right one to deal with the complexity of the department.”

Sen. John Marty, the ranking Democrat on Benson’s committee, said very few people would be right for the job. “He cares a lot about human services issues but caring about them and being commissioner are two different things,” Marty said of Lourey.

Lourey was one of the Legislature’s top experts on human services before Walz appointed him in January, costing Democrats a seat in a Senate with a razor thin GOP majority that grew when a Republican won Lourey’s seat in a special election.

Wheelock served as finance commissioner under Gov. Jesse Ventura. She has a lengthy resume of high-profile positions, including deputy mayor in St. Paul, vice president at the University of Minnesota and a top official in the Minnesota Wild’s early years.