Teachers are escalating their confrontations with students after learning they’re on the brink of being suspended over the school’s handling of a class dispute.

In a letter sent Wednesday to parents, the American Federation of Teachers said it was “inundated” with reports of students “reacting in an unacceptable and unacceptable manner” after learning that their teacher was suspended over a class trip to New York City.

Teachers are responding with what they describe as “an unprecedented level of frustration and fear,” said the letter, signed by teachers from across the country.

The teacher involved, a teacher at the South Shore elementary school in Lakeview, Ill., was suspended and later fired.

The Chicago Teachers Union, which represents more than 12,000 Chicago public school teachers, has also accused the district of ignoring the district’s own internal investigation.

The teachers union says its members have been subjected to verbal and physical abuse.

In recent weeks, more than a dozen teachers have left their jobs in the South Side neighborhood of Forest Hills in the wake of the dispute.

Chicago Public Schools declined to comment on the teachers’ union allegations.

The district has also received numerous reports of violent incidents involving students at other schools.

In September, a 19-year-old high school senior was shot to death by an 18-year old student in a Chicago public elementary school after he pulled a gun and threatened a classmate, according to the Cook County medical examiner’s office.