CHICAGO (AP) - The Supreme Court's ruling in an Illinois labor case gave Republican Gov. Bruce Rauner a rare victory in his campaign to weaken public-worker unions and something to tout in a tough re-election battle.

It also has fired up unions and their Democratic allies who are looking to stop him.

The court on Wednesday said public employees can't be forced to pay fees to labor unions that represent them in collective bargaining. The decision is expected to financially weaken unions and affect millions of government workers

Rauner, who faces billionaire businessman J.B. Pritzker in November, filed the initial lawsuit challenging the fees shortly after taking office in 2015. He traveled to Washington D.C. in anticipation of the decision, which he called a "historic victory."

"This ruling is pro-worker and pro-taxpayer," Rauner said. "State employees - union and non-union - do tremendous work for the people of Illinois. This ruling is a great victory for our democracy, our public employees, and the taxpayers who count on us to bargain on their behalf."

Rauner was joined on the court steps after the decision was issued by Mark Janus, a child support specialist for the state who took over as plaintiff, and members of the Liberty Justice Center, the legal affiliate of the conservative Illinois Policy Institute. The organization represented Janus along with the National Right to Work Legal Defense Foundation.

Pritzker said he was "appalled" by the decision, and called it "another example of Rauner partnering with anti-worker special interest groups" like the Illinois Policy Institute "to pursue his own agenda over the best interests of working families."

"The fight is far from over," said Pritzker, who has received early, strong support from Illinois unions. Some union members stood with him in Springfield Wednesday, where Pritzker said that while the decision will win Rauner some backing "the vast majority of people in Illinois know this decision is bad for them."

Labor has historically wielded significant political might in Illinois. But despite spending more than $10 million in 2014, the unions were unable to stop Rauner - a wealthy former private equity investor - from becoming the first GOP Illinois governor in more than a decade.

The lawsuit against the American Federation of State, County and Municipal Employees Local 31 was one of the first attacks Rauner launched against organized labor after railing throughout the campaign about public-employee unions and their "union bosses."

That same day, Rauner issued an executive order directing that the state put the so-called "fair share fees," collected from about 6,500 state employees' paychecks, into an escrow account rather than forwarding them to unions. His office said it could keep an estimated $3.75 million from being deposited into the unions' bank accounts.

He later relented on the order after objections from unions and the Democratic attorney general. He was replaced as plaintiff in the case after a judge ruled he didn't have standing to sue.

The fees, which are lower than members' dues, are intended to cover the cost of nonpolitical union activity such as collective bargaining. Unions argued they guard against "free riders," or workers who benefit from union representation but don't contribute to the cost of providing it.

Rauner argues all public-worker union activity is inherently political, because unions negotiate contracts and other issues with the same office holders they either help elect or fight to defeat.

He saw the case as a fundamental piece of his strategy to transform Illinois government by making public-worker unions less powerful - a mission that's been largely thwarted by a Democratic-controlled Legislature.

Rauner's office said the state would notify employees of the decision Wednesday and workers would be given the opportunity to leave the union. Illinois also will stop withholding the fees from non-union members' paychecks.

"The worker now has the ability to make his own decision or her decision, and that's why I brought this case," Janus said from the Supreme Court steps Wednesday.

Unions, expecting the ruling, have stepped up recruiting and education efforts in recent months and been holding pro-labor rallies in Chicago and other cities. They pledged Wednesday that their efforts will not let up.

"We are more resolved than ever to fight like hell to win for our members and the communities they care so much about," AFSCME President Lee Saunders said.