Slidell — A junior high social studies teacher fired by the St. Tammany Parish school system last year over a controversial display of student political cartoons is suing his former employer.

Robert Duncan, who taught at Boyet Junior High School in Slidell for 13 years, claims in the lawsuit filed last month that he was unfairly terminated and that his rights under the school system’s collective-bargaining agreement were violated.

He’s seeking reinstatement and back pay.

Duncan was fired in August following a controversy earlier in the year involving a student’s cartoon artwork of President Barack Obama with a mark on his temple that has been interpreted as a bullet hole.

Duncan denied the mark was on the student’s work when it was turned in or when he posted it along with other cartoons in the school’s hallway in January 2012.

A tenure hearing in August was interrupted by Hurricane Isaac and did not resume until November.

Shortly after that hearing, a three-member review panel threw out all but seven of the 20 charges against Duncan, his attorney Charles Branton said. But the panel upheld his dismissal.

Branton said the school system terminated his client under a new law that was part of Gov. Bobby Jindal’s education overhaul, which substantially changed teacher tenure law.

Disciplinary proceedings against Duncan were already under way when the state Legislature adopted those changes. Branton argues the old rules, rather than the new, should have been used.

Branton also pointed out in an interview Thursday that just this week, a state judge in Baton Rouge declared the new law unconstitutional, which means the state Supreme Court will decide whether the changes stand.

If the law is ultimately found to be unconstitutional, Branton argues, his client would be entitled to a new hearing before the entire St. Tammany Parish School Board.

The lawsuit maintains that school officials violated Duncan’s rights in several ways, including failing to provide him written notice of the reason for the disciplinary action prior to his initial hearing before Boyet’s principal, Mitchell Stubbs.

The suit alleges that one of the review panel members, Regina Sanford, was involved in creating the charges against Duncan and suggesting evidence, making it impossible for her to act impartially. It also says that Harry Pastuszek, the school system’s lawyer, produced documents at the August tenure hearing that had not been previously provided to Duncan “and proceeded to have a trial by ambush.’’

Meredith Mendez, spokeswoman for the St. Tammany Parish school system, said she could not comment on a personnel matter.

The lawsuit alleges that Terrie Mathison, an assistant principal at Boyet, testified at the tenure hearing that Stubbs told her he had found Duncan not guilty after the initial hearing. The lawsuit argues that should have been the end of the matter.

“Who told him to change his mind?”’ Branton asked Thursday. “The fix was in. This guy got railroaded.’’