The Big Apple’s powerful teachers union returned to court Friday to press its case that New York’s new class size law should prevent co-location of two charter schools in public school buildings.

The legal drama is the latest entry in the bitter and long-running battle between the United Federation of Teachers and Success Academy, the city’s largest charter school network, which is headed by Eva Moskowitz, one of the union’s most vocal critics.

In its lawsuit, the UFT cited a new class-size law to try to invalidate the co-location of two Success Academy charter schools at public school buildings in Queens and Brooklyn.

Charter schools are legally allowed to occupy vacant space in Department of Education buildings and have done so for years.

The 52-page legal challenge contends that the Department of Education failed to consider the impact of the state’s new law capping class sizes when approving the charters — and that the regulations will require more space in DOE schools, meaning the charters would not fit.

The law, which limits the number of students in classes from kindergarten to 12th grade, has four major exemptions that the Department of Education can use to sidestep the mandates, sources said.

The exemptions cover: lack of space, “over-enrolled” programs, a shortage of licensed teachers, and schools in “severe economic distress.”

Manhattan Supreme Court Justice Lyle Frank told the courtroom that he planned to rule quickly in the case, but did not provide anymore detail about when he would issue his decision, several people in attendance said after the hearing afternoon hearing wrapped up.

“We are confident that this judge will do the right thing, which is to allow these schools to open so the families who have chosen them can send their children to a school of their choice,” said Ann Powell, the top spokeswoman for Success Academy.

All told, the UFT and anti-charter school allies have filed more than a dozen lawsuits against Success over the past decade. None has been successful.

Proponents say that gives them flexibility to try new teaching tactics and curriculum, helping many schools to post impressive results on the state’s tests.

The UFT and its allies argue that charter schools are allowed to impose strenuous criteria on admissions and students, which allow them to dump children with behavior or learning problems back into the public school system.

A spokeswoman for the UFT did not respond to a request for comment.