NEW YORK — New York City will require proof of COVID-19 vaccination for all Department of Education workers, from teachers to custodians to agency office staff, beginning Sept. 27.

Mayor Bill de Blasio announced the vaccination mandate Monday, three weeks before the beginning of the school year on Sept. 13. The mandate, unlike a broader requirement for all municipal employees, does not include an option to test weekly for the coronavirus instead of receiving a vaccination.

The mandate affects 148,000 staff, including contractors who work in schools. About 63% of education department staff have received at least one dose of the vaccine, the city said.

"I feel confident that this is going to work," de Blasio said at a news conference. "We're going to see a lot of our teachers and other school staff get vaccinated as a result of this mandate."

The city said that the rule followed guidance from the CDC issued earlier this month that recommended teachers and staff be vaccinated “as soon as possible.” 

Though education staff will have two weeks after the school year starts to get their vaccination before the mandate goes into effect, de Blasio said that other school safety measures, such as mask-wearing and vaccinated students, will help keep students safe. He said that the city would release a handbook for parents on school safety within the coming days. 

The vaccination rule comes the same day as the U.S. Food and Drug Administration announced full approval for the Pfizer vaccine, giving states and cities stronger footing for vaccination mandates. 

The new mandate also comes as de Blasio has strengthened vaccination requirements for city workers in recent weeks, with a blanket test-or-vaccinate rule going into effect on the first day of school.

De Blasio has repeatedly said he is considering further rules to “climb the ladder” of COVID-19 precautions with cases on the rise since mid-June.

"In the days ahead we'll be looking at the rest of the workforce," he said Monday in response to a question about a wider vaccine mandate.

He said he is not considering a vaccine mandate for students because the city does not want to create any "impediments" to students returning to classes, although students and coaches in the Public School Athletic League in high-risk sports are required to vaccinate.

The new rules, alongside vaccination incentives such as a $100 gift card on your first dose at a city-run clinic, have spurred city immunization rates higher after they began to plateau in the spring. Just under two-thirds of city adults are fully vaccinated, according to city data.

De Blasio said he had discussed the rule with union leaders in recent days, but acknowledged that some details of the rule remained to be negotiated with unions. 

"I think everyone understands we're in a crisis, and vaccination is the answer," he said.

Unions of public employees have shown a mixed response. DC37, the city's largest public union, said that it did not believe the mayor had the "legal authority to change the terms and conditions of employment without bargaining," and would be filing an unfair labor practices complaint alongside a coalition of other unions.

The United Federation of Teachers, which represents city public school teachers, signaled its support for the rule — and for the mayor's ability to make such a rule — but said the details still need to be worked out. 

"While the city is asserting its legal authority to establish this mandate, there are many implementation details, including provisions for medical exceptions, that by law must be negotiated with the UFT and other unions, and if necessary, resolved by arbitration," Michael Mulgrew, president of the UFT, said in a statement.

Speaking on "Inside City Hall" in his weekly "Mondays with the Mayor" segment, the mayor countered DC37's statement.

"The fact is, I've talked to the labor leaders involved and I told all of them we would bargain immediately, impact bargaining starting immediately this week, and this is for a policy that doesn't take effect until Sept. 27," de Blasio told NY1 political anchor Errol Louis. "I'm confused myself, because when I said this morning in the press conference we were immediately going to go to bargaining, I thought that was pretty clear."