The 2011 law, known as Act 10, imposed a near-total ban on collective bargaining for most public employees. It has withstood numerous legal challenges and was the signature legislative achievement of former Republican Gov. Scott Walker, who used it to mount a presidential run.

The law catapulted Walker onto the national stage, sparked an unsuccessful recall campaign, and laid the groundwork for his failed 2016 presidential bid. It also led to a dramatic decrease in union membership across the state.

If the latest lawsuit succeeds, all public sector workers who lost their collective bargaining power would have it restored. They would be treated the same as the police, firefighter and other public safety unions who remain exempt.

The law is “fundamentally unequal,” irrational and unconstitutional, unions argue in court filings.

The Republican-controlled Legislature is asking for the case to be dismissed, arguing that “it has long been settled that Act 10 passes constitutional muster.” Dane County Circuit Judge Jakob Frost scheduled arguments on the motion to dismiss for Tuesday.

The Legislature also argues that the unions waited too long to bring the challenge, noting that the law has been in effect for nearly 13 years and survived state and federal court challenges.

The lawsuit says that exemptions for firefighters and other public safety workers are unconstitutional, similar to arguments made in an earlier case brought by teachers and Milwaukee public workers that was rejected in 2014 by the state Supreme Court.

The only change since the Wisconsin Supreme Court’s 2014 ruling is the makeup of the court, attorneys for the Legislature said in court filings.

“And that is certainly no reason for any court in Wisconsin to depart from that precedent,” the Legislature argues.

The court is controlled 4-3 by liberals, a flip from when it upheld the law a decade ago under 5-2 conservative control.

The state Department of Justice, overseen by Democratic Attorney General Josh Kaul, is representing state agencies named as defendants and also supporting dismissal of the case.

The Act 10 law effectively ended collective bargaining for most public unions by allowing them to bargain solely over base wage increases no greater than inflation. It also disallowed the automatic withdrawal of union dues, required annual recertification votes for unions, and forced public workers to pay more for health insurance and retirement benefits.

Teachers and other public workers argue in their lawsuit that Act 10 violates the Wisconsin Constitution’s equal protection guarantee and exempts groups that also endorsed Walker in the 2010 gubernatorial election, while those subject to the restrictions did not.

But the Legislature and state agency defendants all say there were rational, legal reasons for differentiating the groups of employees.

A federal appeals court in 2013 also rejected claims that the law violated the equal protection guarantee in the U.S. Constitution, saying 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.

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.

The defendants cite those previous rulings in arguing for dismissal. The unions argue that their case raises different legal issues than those past lawsuits that failed.