Lawyers for accused subway gunman Frank James’ claimed the FBI may have violated his rights by taking DNA swabs from him in his Brooklyn jail cell without notifying them first, according to a Thursday court filing.

In a letter, attorneys Mia Eisner-Grynberg and Deirdre von Dornum said FBI agents went into James’ cell on Tuesday, took the oral DNA swabs, questioned him and forced him to sign documents. 

“Contrary to standard practice, the government committed this intrusion absent advance notice to counsel, depriving us of an opportunity to be heard or to be present,” they wrote. 

It’s common to inform the attorneys of a suspect who has been arraigned that a search warrant for DNA swabs has been obtained, the filing notes.

“Here, because the government failed to provide notice to counsel before questioning and searching Mr. James, their practice risked violations of Mr. James’s core constitutional rights under the Fourth, Fifth and Sixth Amendments,” the attorneys wrote. 

The lawyers may file a suppression motion asking a judge to exclude that evidence because of the “potential constitutional violations,” they said.

Federal prosecutors said that contrary to “hyperbole” on the part of James’ lawyers, “his DNA was obtained pursuant to a judicially authorized search warrant and no violations of any of the defendant’s constitutional rights occurred in the execution of the warrant.”

James is accused of spraying 33 bullets into a crowded subway train in Sunset Park on April 12 after letting off a smoke bomb that filled the car with fumes.

The alleged terror attack left 29 people injured, including 10 who were shot.

James, who was arrested following a 30-hour citywide manhunt, was charged in federal court with terrorism on a mass transportation system. He faces life in prison if convicted.