The city and state teachers unions are suing to block a charter high school from bringing a prestigious international diploma program to the Bronx.

The New York State United Teachers and United Federation of Teachers assert that the establishment of the Vertex Partnership Academies would violate the current state cap of 290 city charter schools.

Their suit contends that the new school — founded by prominent charter advocate Ian Rowe — is trying to “circumvent” the cap by drawing students from two existing charter schools and casting itself as an expansion.

“Put simply, if it looks like a new charter, is held accountable like a new charter, and is structured like a separate and new charter, then it is indeed a new charter and not an expansion,” the lawsuit states.

UFT boss Michael Mulgrew, a staunch opponent of charter schools, echoed that opposition.

“This is a clear end run around the charter cap,” he said in a statement. “Once again, the charter sector is acting as if the rules don’t apply to them. We are here to say you have to follow the law.”

Charter school backers argue that parents, especially those in areas with academically grim schools, should have the same educational choices as more affluent New Yorkers.

According to the Vertex website, the school would establish an International Baccalaureate program for Bronx kids.

Developed in Switzerland, the program offers internationally recognized diplomas that give graduates the chance to enroll at top domestic and global universities.

“Vertex student scholars will be immersed in a culture of democratic discourse guided by the four cardinal virtues of Courage, Justice, Wisdom, and Temperance,” the site states.

But NYSUT chief Andy Pallotta said that the school is finessing state rules in order to elude the cap and must be stopped.

“The SUNY Trustees and their Charter Schools Institute may think this scheme to create new charter schools is clever, but the law is still the law,” Pallotta said in a statement. “Those who view the charter cap in New York City as a suggestion instead of a statutory mandate are living in a fantasy land. We look to the courts to give them a reality check.”

The unions asserted that the State Education Department and Board of Regents said the school was “clearly violating state law” and that “that SUNY itself is treating the high school as if it’s a new charter, requiring accountability measures that in SUNY’s own words are ‘normally reserved for new schools.'”

The proposed school’s founder, Ian Rowe, graduated from Brooklyn Tech and led the Public Prep charter school network for ten years.

He was not immediately available for comment.

State lawmakers, along with Gov. Kathy Hochul, have declined to raise the city’s charter cap.