Last week’s sudden order from Gov. Gavin Newsom directing workers back into offices four days a week has provoked a legal response from labor unions: They have filed “unfair practice” charges with the California Public Employment Relations Board over the new mandate.

That could trigger a complaint by the board and eventually force a formal hearing on the matter in front of an administrative law judge.

Ted Toppin, the executive director of the Professional Engineers in California Government, described the recent change as “inexplicable and unnecessary.” The union primarily represents Department of Transportation employees.

“It really is trying to end a win-win situation,” Toppin said. “The work is getting done. The people’s business is being performed without fail.”

The engineers group and SEIU Local 1000, the largest public sector union in the state, have both filed charges.

Anica Walls, SEIU Local 1000’s president, said in a statement the union is demanding that the employment board rescind Newsom’s order immediately.

“Agencies should be making operational decisions based on business needs — not political mandates.”

The Governor’s Office did not immediately respond to a request for comment.

Newsom’s order directed agencies and departments under his purview to make the schedule change by July 1. His office said more than half of the state’s roughly 224,000 full time workers already report to work in person every day.

Many of those affected have also expressed frustration and confusion over the timing of the decision.

The unions allege that the new mandate violates the Ralph C. Dills Act, which outlines labor regulations between the state and public employees, in several ways.

They argue Newsom doesn’t have the unilateral authority to implement the new policy, which they say will also remove employee telework stipends. And they said the groups should have had a chance to discuss the order with state officials before the governor issued it.

In their filings, the unions said their current agreements with the state cover roughly 105,000 employees combined. Both groups are asking for the employment board to tell the state to rescind Newsom’s order.

Last year, a labor arbitrator ruled that state agencies can require their employees to come to the office even if their union contracts give them the right to work from home, according to CalMatters.

Unions have announced other actions in response to the governor’s recent order.

The California Association of Professional Scientists said it wants to bargain over what exemptions will be allowed under the new mandate. The group and SEIU Local 1000 are also planning to picket outside offices across the state on Wednesday.