Public sector unions and the Province of Manitoba head to court Tuesday in a battle over legislation that would would impose a two-year wage freeze on all government workers.

More than a dozen unions, representing about 110,000 workers, nurses, teachers, and other government employees, say the Public Services Sustainability Act violates their constitutional right to collective bargaining.

On Sunday, the unions held a rally on the steps of the Legislative Building to voice their opposition to the law.

"This government's wasting valuable resources to spend time in court. They're delaying doing bargaining, they're denying workers being able to keep up with inflation. And they're avoiding a process that works," said Kevin Rebeck, president of the Manitoba Federation of Labour.

The government passed the legislation in spring 2017, but hasn't proclaimed it. It freezes wages for the first two years for all new contracts, followed by a 0.75 per cent increase in the third year and a one percent increase in the fourth year.

The government rejects the notion that the act violates collective bargaining, arguing the province's high deficit, rising expenditures and increasing debt servicing costs give the government the legislative right to enact laws dealing with the labour relations and fiscal issues in the public interest.

Tom Lindsey, NDP MLA for Flin Flon, called attention to the rally during question period on Monday and asked the government to repeal the act.

"Contrary to what this government might like us to believe, it wasn't just union folks out there, but it was concerned citizens, and this marked the beginning of the legitimate court challenge to Bill 28," The Public Services Sustainability Act, he said.

Finance Minister Cameron Friesen called the act a "moderate" piece of legislation that was needed to help deal with a growing deficit that had reached $1 billion.

"Public sector labour costs in Manitoba comprise a very significant portion of government expenditures. As has been the case for decades, government sets a bargaining mandate for public sector employers establishing broad parameters for negotiations between parties," Friesen said in an emailed statement.

"Contract negotiations continue in all public sector areas while this motion is before the courts."

In their statement of claim, the unions say that the law violates employees' rights under the Charter of Rights and Freedoms by "forcing them to work under terms and conditions of employment which were coerced, dictated and imposed by the state."

The province's statement of defence says the act respects collective bargaining by not reopening existing agreements and allowing collective bargaining to continue on a variety of workplace issues, such as working conditions, health and safety, and job security.

It also says the act "allows for an increase in wages if real savings can be realied through negotiated efforts ... with Treasury Board approval."

The unions' statement of claim also cites evidence from a Manitoba Labour Board hearing into whether the provincial government interfered with negotiations between the University of Manitoba and faculty members by directing it to impose a one-year wage freeze.

In January 2018, the board ruled the university had engaged in unfair labour practices, and earlier this month the university apologized.