The federal government has sued the New York City Department of Education over the alleged racist actions of a high school principal, arguing that city officials allowed the principal to systematically discriminate against black teachers — and to retaliate against an assistant principal who pushed back.

“It is nearly unthinkable that, in this day and age, one of the largest and most diverse school districts in the United States would allow racial discrimination and retaliation to flourish. Yet that is what we allege happened at Pan American International High School,” said Manhattan U.S. Attorney Preet Bharara, whose office filed the complaint in federal court Thursday.

Devora Kaye, a spokeswoman for the New York City Department of Education, said the department has “zero tolerance for any discrimination” and “all employees’ work environments must be safe and supportive.”

The complaint accuses Minerva Zanca, the now-retired principal of Pan American International High School in Queens, of referring to black teachers’ “big lips” and “nappy hair,” and of saying that one black teacher “looked like a gorilla in a sweater.”

The complaint also alleges that Zanca targeted untenured black teachers with poor performance reviews, saying it was the best way to push them out. The suit said she told her assistant principal, Anthony Riccardo, that she intended to give those teachers poor ratings before she saw the lessons she was supposed to evaluate.

When Riccardo refused to give an unsatisfactory to one of the black teachers, Zanca accused him of “sabotaging her plan,” according to the complaint, and then called security to remove him from the school.

Zanca said that the allegations are false. “I did not make those reprehensible and disgusting comments, and I’m outraged that they were attributed to me,” she said in an interview Friday.

She accused Riccardo of manufacturing the allegations because he was a disgruntled employee, angry at her for her role in referring him to internal investigators with the city education department. Those investigators ultimately found no reason to charge Riccardo, according to the federal complaint.

Of the 27 teachers at Pan American International High during the 2012-2013 school year, three were black, according to the complaint.

Two were untenured and subject to dismissal if they received an unsatisfactory evaluation. The third, who was tenured, taught the school’s theater courses and oversaw its theater productions. In February 2013, on the day of the first student play of the year, the suit said, Zanca told the teacher that she would have to cancel that production because the school would not foot the bill for all of its associated costs. The show went on only because the teacher paid out of her own pocket, according to the complaint.

All three black teachers received unsatisfactory job ratings in 2012-2013. The two untenured teachers were let go, and the tenured teacher remains employed by the district. Riccardo, the assistant principal, also received an unsatisfactory rating. He resigned.

The three teachers and Riccardo took their complaints to the city’s Office of Equal Opportunity and eventually to the U.S. Equal Employment Opportunity Commission. But before any of their investigations began, according to the complaint, Zanca’s supervisor wrote in an email to colleagues that the allegations were “unfounded” and that Zanca “deserves our support.”

The city’s Office of Equal Opportunity stopped investigating once it learned that the federal EEOC was considering the same case. In October 2013, one of the black teachers sued the city’s Department of Education, alleging discrimination on the basis of race. In May 2014, the federal EEOC found “reasonable cause” to believe that the other two teachers and Riccardo had experienced discrimination and retaliation.

Zanca was not disciplined, and she continued to serve as principal at Pan American International for two more years before retiring in 2015.