A federal appeals court Monday made way for New York Mayor Bill de Blasio (D) to implement a coronavirus vaccine mandate for all school employees, ruling against four educators who had sued to stop it.

The court decision marks a major victory for the nation’s largest school system, which employs 150,000 people and educates over 1 million students in a city gutted by the coronavirus last year. Unlike most other cities, New York’s mandate does not allow employees to submit to regular testing as an alternative to getting a vaccine.

The city’s mandate would have required all school employees to show proof of at least one shot by midnight Monday. But on Friday, a judge for the U.S. Court of Appeals for the 2nd Circuit issued an injunction temporarily halting the requirement.

On Monday, a three-judge panel denied the injunction, clearing the path for the mandate to go in to effect.

The New York Times first reported the development.

Despite the ruling, the city said it would give school employees until the end of the day Friday to show proof of vaccination. About 13 percent of all school employees are not vaccinated, including about 9 percent of teachers and 3 percent of principals, school officials say.

According to the United Federation of Teachers, the city’s education department plans to remove employees who have not obtained an exemption or shown proof of vaccination from the payroll.

Mark Fonte, one of the attorneys representing the educators who sued, said in an emailed statement that he and his co-counsel are petitioning the U.S. Supreme Court for emergency relief. In their lawsuit, they argued that the severity of the consequences for refusing the vaccine “shocks the conscience, violates constitutional rights, and not only should not be permitted but must be restrained immediately to prevent irreparable harm.”

On Monday, Fonte said he is “dismayed and disappointed by this turn of events.”

“With thousands of teachers not vaccinated the City may regret what it wished for,” Fonte wrote. “Our children will be left with no teachers and no security in schools.”

Many districts give school staff the option to get vaccinated or submit to regular testing. But as the pandemic wears on, more jurisdictions are making it mandatory — with no option to forgo the vaccine — for everyone except for those who obtain medical or religious exemptions. The showdown in New York over the mandate may foreshadow other court fights.

Last week, the District implemented such a mandate, telling unvaccinated school employees and child-care workers they could no longer submit to testing if they did not want to get the vaccine. Oregon, Washington and Puerto Rico also have mandates without testing options, according to EdWeek.

Michael Mulgrew, president of the United Federation of Teachers, said he and his members remain concerned that the New York mandate could leave schools shorthanded.

“We will be working with our members to ensure, as far as possible, that our schools can open safely as the vaccine mandate is enforced,” Mulgrew said Monday in a statement.