Dozens of New York City teachers were officially placed on unpaid leave Monday after allegedly using fake vaccination cards.

The suspected teachers were notified last week that they would be placed on unpaid leave by the city's Department of Education after police confirmed the teachers used fake vaccination cards.

“Fraudulent vaccination cards are not only illegal, they also undermine the best line of protection our schools have against COVID-19 — universal adult vaccination,” Nathaniel Styer, a spokesperson for the Department of Education, said in a statement.

“We immediately moved to put these employees — fewer than 100 — on leave without pay," Styer said.

The United Federation of Teachers believes that the unpaid leave is a violation of its bargaining agreement. It plans to challenge the Department of Education’s move by demanding that the employees with current disciplinary actions stay on the payroll.

“It is wholly improper for the D.O.E. to unilaterally remove U.F.T. members from the payroll based on mere conjecture that vaccination documentation is fraudulent,” Beth A. Norton, a lawyer for the union, wrote in a letter to the department last week.

The incident is being investigated by law enforcement and the Special Commissioner of Investigation for the New York City School District, according to Styer.

The New York Times’ tracker shows that New York City’s coronavirus cases have risen 55% in the past two weeks.