ALBANY – The state’s largest teachers union is suing New York State in an attempt to have the property tax cap declared unconstitutional, setting the stage for a protracted legal and political battle.

New York State United Teachers, or NYSUT, said the cap violates the state constitution by perpetuating funding inequalities between rich and poor school districts and violates “one person, one vote” protections.

The 600,000-member union filed a lawsuit Wednesday in State Supreme Court here in an effort to overturn the law that caps the annual growth of local property taxes at about 2 percent, unless 60 percent of local voters agree to tax beyond the cap.

“This is not about raising property taxes,” NYSUT President Richard C. Iannuzzi said in an interview. “This is about the state equitably funding education.”

Thousands of teachers have lost jobs since the tax cap and economic pressures forced school districts to cut costs. The union timed its lawsuit to the start of budget talks at the Capitol over state aid for public schools.

While Senate Republican leader Dean G. Skelos, of Nassau County, said the lawsuit is without merit, another group of Democratic and Republican lawmakers called on Gov. Andrew M. Cuomo to increase funding for the state’s nearly 700 school districts – 87 percent of which have let teachers go in the last couple of years.

An upstate business group that helped push for enactment of the tax cap sharply criticized the union’s lawsuit.

“Once again, NYSUT is showing its disdain for taxpayers. New York State continues to have some of the nation’s highest property taxes, and the tax cap was the first step toward addressing this crisis,” said Brian Sampson, executive director of Unshackle Upstate.

He noted that 95 percent of the state’s schools stayed within the cap level in their first round of school budget votes last year.

With personnel costs amounting to at least 75 percent of district expenses, school officials for years have been pressing Albany to reduce state-imposed mandates, such as the Wicks Law, which drives up construction costs by requiring multiple prime contractors on projects.

Another mandate, the Triborough Amendment, permits salary “step”’ increases to proceed when teacher contracts expire, giving little incentive for NYSUT locals to cut deals to help reduce wage and benefit costs.

By setting caps on how much a district can raise in property tax revenues, the tax cap law keeps in place “funding inequities” between wealthy districts and those that serve low-income families in urban and rural districts, NYSUT contends.

The lawsuit alleges seven causes for the action, including that the provision allowing 60 percent of a district’s voters to override the cap is unconstitutional. During the tax cap debate before the law was passed, the union had sought to override attempts to be successful on a simple majority – 50 percent plus one vote – in annual school budget votes.

The union says the 60 percent rule means that someone wanting to override the cap has only two-thirds the voting power of opponents.

Voter anger over rising taxes, implementation of the tax cap and a sour economy have prompted districts across New York to cut programs and staff positions over the last couple of years.

The New York Council of School Superintendents recently reported that districts, on average, have cut 9 percent of their positions over the last two years and that 59 percent increased student class sizes this year.

Eighty-four percent of schools are getting less state aid than they did in 2008, and 9 percent of superintendents statewide – and 12 percent of those in Western New York – believe that their districts could face insolvency in the next two years.

Many localities, which are also subject to the tax cap provisions, say they increasingly are feeling fiscal strains during a period of flat-line state aid and limits on how much they can ask local voters to fund state-imposed costs for expenses such as employee pensions and social service programs.

Cuomo, the prime backer of the tax cap, has insisted that the property tax program is not a cap, since it does allow local voters to exceed the level if 60 percent of them say so.

“People have a right to go to court. God bless America. God bless our system,” Cuomo said.

But he defended the tax cap as one of the most important changes that his administration has achieved and rejected NYSUT’s call for more state aid to schools. “The answer can’t always be putting the hand in the pocket of the taxpayers of New York,” Cuomo said. “… The answer that it’s more money, more money, more money, I reject.”

The cap is not a straight cap on each homeowner’s property taxes, but rather on the total property tax levy for a district or locality in a given year. There are also spending exceptions to the cap, which means that the actual cap can – and has gone – above the 2 percent level in most communities.

The NYSUT challenge is a serious one because it is a well-funded union with the resources to see the court challenge through to the end.

If the courts reject the cap, it would be a political blow to Cuomo, who is up for re-election next year and who made the tax cap plan one of his signature policy initiatives in his first term.

NYSUT says the state has failed to live up to the decision of an historic school funding lawsuit resolved in 2007, when Albany agreed to spend an additional $7 billion on “low-wealth” districts by 2011. Only $2 billion of that level was spent, NYSUT alleges. Cuomo’s 2013 budget proposal allocates about $300 million less on public schools than the 2008 level, the union contends.

Most school districts were averaging tax increases of about 3 percent per year in the few years before the tax cap was enacted, but Albany’s funding commitment to schools is inadequate, according to the union.

“There needs to be a very serious discussion that New York keeps punting down the road on how to fund education,” Iannuzzi said, adding that schools have shed 30,000 positions in the last few years.

While NYSUT wants the state to increase aid to schools as a way to help districts rely less on property taxpayers, districts over the years have said NYSUT has made the situation worse by opposing state mandate relief that would reduce expenses for schools.

In its legal challenge, NYSUT says funding differences between schools is attributable to assessed property values that vary dramatically across the state.

It noted that the amount districts spend per student ranges from $23,000 at one North Country school to $36,000 at the Southampton district on Long Island.

The way the tax cap is structured, NYSUT says, local control of school financing is undermined, a protection that the state’s highest court has upheld in past cases.

The union says the cap is also flawed because wealthier districts can afford to break the tax cap, leading to further inequities between rich and poor communities.

The union also calls illegal the tax cap law’s “poison pill” that sets spending levels if 60 percent override results are not achieved in two separate referendums. That, according to the union, has a “chilling effect” on voters who want to spend beyond the cap’s level.