An Alameda County Superior Court judge Thursday ordered Gov. Arnold Schwarzenegger to halt thrice-monthly furloughs for tens of thousands of state workers, saying the administration overstepped its authority in approving the unpaid days off.

A spokesman for Schwarzenegger said the governor would appeal the decision of Judge Frank Roesch in favor of three state employee unions, including the Service Employees International Union Local 1000. The unions had filed suit after the governor began the furloughs in February, in response to a multibillion-dollar budget shortfall.

The judge ruled that the governor’s use of the state Emergency Services Act to furlough state workers because the state did not have a budget at the time had limits.

“The emergency necessitating them was the failure of the Legislature to pass the budgets, though the reach of the orders extended long after those budgets were subsequently passed and signed into law,” the judge wrote. Roesch also ruled that furloughing state employees who are paid from special funds interferes illegally with the operation of specially funded agencies.

He said that the governor’s use of furloughs was an “abuse of discretion” and that he “violated a mandatory duty to take into account the agencies’ varying needs before reducing workplace hours.”

The governor plans to appeal Roesch’s decision and noted that the order blocking the furloughs would be stayed until the appeal is ruled on, said Aaron McLear, a spokesman for Schwarzenegger.

“Ultimately this will be decided by the state Supreme Court,” McLear said. “The governor absolutely has the authority to issue furloughs, and we feel the state Supreme Court will rule in our favor.”

The lawsuit was also filed by the California Attorneys, Administrative Law Judges and Hearing Officers in State Employment and the Union of American Physicians and Dentists.

The judge ordered the governor to “cease and desist” the furlough of specific employees.

The furloughs were pitched by the governor as a way to reduce the shortfall in the state general fund, but the judge noted that it affected workers paid by separate special funds, including those who handle Social Security disability claims and those in Department of Motor Vehicles offices funded with license fees.

The judge’s order affects at least 52,000 state workers represented by SEIU, according to Yvonne Walker, the union’s president.

“I am ecstatic. I’m feeling vindicated,” Walker said. “We said all along that the governor’s actions were illegal.”

The union had negotiated a contract with a 5% pay reduction, while the furloughs had the affect of cutting pay by nearly 15%, Walker said.

State Senate President Pro Tem Darrell Steinberg (D-Sacramento) agreed with Walker that the governor should return to the bargaining table and negotiate an agreement with the unions.

“The court ruling issues a clear directive to the governor: Sit down and negotiate with state employees to develop a rational labor agreement,” Steinberg said. “State employees can help find budget savings that won’t make hard-working people bear all of the sacrifice and deprive Californians of critically important public services.”

patrick.mcgreevy@latimes.com