The United Federation of Teachers is suing to stop a charter school from invading PS 114’s building, putting a monkey wrench in the two-month old “separate-but-equal” compromise between school officials and the city that saved the beleaguered elementary school.

In court papers filed on May 18, the union, the NAACP and several elected officials claimed that the Explore Charter School — which is set to open inside the century-old Remsen Avenue building near Glenwood Road in September — has been given permission to use building’s gym and playground for longer periods than PS 114 students will, even though the charter’s enrollment of 240 only makes up one-third of the building’s student body.

UFT President Michael Mulgrew said that the disbursement of space at PS 114 is far from equitable — and possibly illegal.

“[The city] is violating the state law that governs co-locations, ignoring its obligation to make sure that district school children have the same access to public facilities as do charter schools,” he said.

Councilman Charles Barron (D-Canarsie), who is a co-plaintiff on the UFT lawsuit, agrees.

“We can’t trust the Department of Education,” Barron said. “They play a lot of bait-and-switch games, and this co-location chaos will really damage our teacher’s ability to implement a quality education.”

But PS 114 would have been closed if not for the deal struck between the city and neighborhood stakeholders. The under-performing public school was spared after teachers and local elected officials grudgingly welcomed the charter school into the building.

PS 114 is one of 20 schools named in the lawsuit expected to set aside space to incoming and expanding charter schools. The UFT is also suing to keep the city from closing more than 20 public schools.

A similar legal challenge stopped the city from closing 15 schools in 2010, UFT members remember. But the city didn’t try to improve these institutions of learning. Instead, it put them on this year’s list of poor performing schools slated for closure

Yet these legal wranglings are weighing heavily on administrators at the Explore Charter School, who hope it doesn’t keep them from opening inside PS 114 this fall.

“It’s really sad that this is the way concerns and questions about our charter schools are getting solved,” explained Explore Schools spokeswoman Lizz Pawlson, who said that more than 700 students have applied to become a part of Canarsie’s first charter school.

Pawlson added that charter administrators and PS 114 staff have already remedied the space disparity outlined in the lawsuit, so all the students have equal time at the playground and in the gym.

“We’re dedicated to equitable school sharing and, based on the response we’re getting, the lawsuit merely demonstrates the needs of the UFT not the wants of the community,” said Pawlson.

The Department of Education could not confirm Pawlsom’s claim by late Tuesday. School Chancellor Dennis Walcott said the UFT’s lawsuit was both “cruel and irresponsible.”

“It will create enormous stress and uncertainty for the 70,000 students matched to high schools this September and the thousands of families who have already gone through the charter lottery process,” he said.