MADISON, Wis. (AP) — A judge’s overturning of Wisconsin’s 13-year-old law that effectively ended collective bargaining for teachers and most state government employees has rekindled a battle over labor rights in a state where the first public sector unions were formed 65 years ago.

But before unions head back to the bargaining table, more legal fights await. Here are five things to know about the law, the current challenge and what happens next:

What is the fight about?

At its core, the battle is over whether tens of thousands of teachers, nurses, prison guards and other state government employees can bargain over their workplace conditions and salary.

The law, known as Act 10, was enacted in 2011 and limits bargaining to only wage increases no greater than the inflation rate. That means that other issues, such as benefits, safety and working conditions, and vacations, are not negotiable.

The law also requires every public sector union to vote annually on maintaining its own certification. In order to pass, at least 51% of each union’s members must vote yes, not just 51% of those voting.

Union members were also required to pay more for their benefits, which reduced their take home pay and effectively served as a pay cut.

Supporters say the law has saved school districts and local governments billions of dollars. Opponents say the law has kneecapped unions that traditionally back Democrats and hurt workers’ morale and income.

Passage of the law helped ease the way for the Legislature in 2015 to approve a so-called right-to-work law that limited the power of private-sector unions.

Who were and are behind Act 10?

Then- Gov. Scott Walker introduced the proposal shortly after taking office in 2011. That sparked weeks of massive protests, a walkout by Democratic state senators in a failed attempt to block passage of the law, and recall elections targeting Walker and Republicans who voted for it.

The fight thrust Wisconsin into the the center of the battle over union rights in the U.S. Walker rode the attention, survived the 2012 recall attempt and then mounted a campaign for president a few years later. He dropped out, though, in the fall of 2015 as Donald Trump’s support grew.

The battle lines then and now are largely the same. The law is opposed by Democrats and unions. It is supported by Republicans, conservative groups and powerful organizations like Wisconsin Manufacturers and Commerce, the largest business lobbying group in Wisconsin.

Haven’t courts already settled this?

Numerous legal challenges have been filed challenging the law in state and federal courts. None of them succeeded until now.

The latest challenge was filed last year by seven unions representing teachers and other public-sector workers and three individuals.

This lawsuit alleges that Act 10’s exemption of some police, firefighters and other public safety workers from the bargaining restrictions violates the Wisconsin Constitution’s equal protection guarantee.

A similar argument was made in a federal lawsuit alleging that Act 10 violated the equal protection guarantee in the U.S. Constitution. But a federal appeals court in 2013 said the state was free to draw a line between public safety and other unions, and the following year again ruled that the law was constitutional.

The Wisconsin Supreme Court in 2014 also upheld the law as constitutional, rejecting a lawsuit brought by teachers and Milwaukee public workers. That case raised different arguments than the current lawsuit. And in 2019, a federal judge rejected a lawsuit brought by two arms of the International Union of Operating Engineers that argued the law violates free speech and free association under the First Amendment.

What are people saying about this latest challenge?

Walker, whose legacy is largely defined by his fight with the unions, called the ruling “brazen political activism.”

The judge who struck down the law, Dane County Circuit Judge Jacob Frost, was appointed by Wisconsin’s current governor, Democrat Tony Evers. It also appears that Frost signed the petition to recall Walker.

Republican leaders of the Legislature echoed Walker’s comments, decrying the ruling and calling Frost an “activist.”

Evers called the decision “great news” and said, “I’ve always believed workers should have a seat at the table in decisions that affect their daily lives and livelihoods.”

Unions applauded the ruling while conservative groups warned that undoing the law would dramatically increase costs on local governments, leading to service cuts and tax increases.

What happens next?

The Legislature has appealed the case. That would typically send it to the state court of appeals, unless the unions ask the Wisconsin Supreme Court to take the case directly.

Opponents of the law are anxious for the state Supreme Court to get the case while it is controlled 4-3 by liberal justices. An election in April will determine whether liberals maintain control or the court flips back to conservatives, who held sway there from before Act 10 was passed until 2023. The newly elected justice will start work next August.

Even if the current court takes the case, it’s unclear what justices would hear it.

Justice Janet Protasiewicz, whose win last year gave liberals the majority, said during her campaign that she believes Act 10 is unconstitutional. She also said she would consider recusing herself from any case challenging the law. Protasiewicz participated in protests against the law and signed the petition to recall Walker.

Conservative Justice Brian Hagedorn was Walker’s chief legal counsel and had a role in drafting the Act 10 law. But during his successful run for the court in 2015, Hagedorn would not promise to recuse himself if a case challenging Act 10 came before the court.