NEW YORK — All New York City public school teachers and other staffers will have to get vaccinated against the coronavirus, officials said Monday as the nation’s largest school system prepares for classes to start next month.

The city previously said teachers, like other city employees, would have to get the shots or get tested weekly for the virus. The new policy marks the first flat-out vaccination mandate for city workers in the nation’s most populous city.

About 148,000 school employees — and contractors who work in schools — will have to get at least a first dose by Sept. 27, according to an announcement from Democratic Mayor Bill de Blasio and the city health and education departments.

The city hasn’t immediately said what the penalty will be for refusing, or whether there will be exemptions. The previous vaccinate-or-test requirement had provisions for unpaid suspensions for workers who didn’t comply.

At least 63% of school employees already have been vaccinated. That figure doesn’t include those who may have gotten their shots outside the city.

School starts Sept. 13 for the city’s roughly 1 million public school students.

It’s not immediately clear how unions representing teachers and other school employees will react. The city Education Department says it’s discussing the matter with them.

The announcement comes as New York and some other cities and states have been fighting the virus’ highly contagious delta variant by ratcheting up pressure to get more people inoculated.

New York City last week began requiring proof of vaccination to enter restaurant dining rooms, gyms and many other public places, a first-in-the-nation policy that a few other cities have copied since it was announced. Meanwhile, New York state announced last week that hospital and nursing home workers would have to get inoculated.

Vaccine mandates for teachers are fairly rare so far in the U.S., though Washington state, for one, says teachers must be inoculated or face dismissal. Vaccinate-or-test requirements are a bit more common.

A new poll from The Associated Press-NORC Center for Public Affairs Research found that about 6 in 10 Americans say students and teachers should be required to wear face masks while in school, and that teachers and eligible students should also be required to get vaccinated. But Democrats and Republicans differ sharply on these issues, the poll found.