NEW YORK — New York City Mayor Bill de Blasio is extending his order requiring COVID-19 vaccines to include teachers and staff at private and religious schools.

De Blasio, a Democrat, said Thursday that employees at nonpublic schools will be required to show they’ve received at least one dose of a vaccine by Dec. 20. The order will apply to about 56,000 employees at 938 schools in New York City.

The Democratic mayor had issued a mandate that took effect in October requiring the shots for workers in the city’s public school system, which is the largest in the country. De Blasio extended the mandates to cover the city’s workforce, including police officers, firefighters and sanitation workers, and broadened the order this week to include child care workers.

“We’re doing everything in our power to protect our students and school staff, and a mandate for nonpublic school employees will help keep our school communities and youngest New Yorkers safe,” de Blasio said in a statement.

City Hall officials said vaccinations will be offered at any private or religious schools that request them and the city will work with school officials to prepare for the mandate’s deadline and ensure they comply.

City officials did not immediately respond to questions about how many of the private school employees are already vaccinated and how the city would enforce the mandate at private schools.

Public school teachers and staff who did not comply with the city’s earlier order were placed on unpaid leave.

Rabbi David Zwiebel, the chairman of the Committee of NYC Religious and Independent School Officials, said in a letter to the mayor Thursday that the committee “firmly opposes” the mandate and urged him to reconsider.

“While we support and generally encourage Covid vaccination in our schools, and while in fact the large majority of our schools’ employees are so vaccinated, most of our schools do not insist upon such vaccination as a condition of employment. Many of our schools view Covid vaccination as a matter most appropriately left to individual choice, not governmental fiat,” Zwiebel wrote in the letter.

He said a small number of unvaccinated employees will likely continue to resist getting the shots and leave schools struggling to fill vacancies.

Most of New York City’s COVID-19 vaccine mandates have been met with legal challenges but were largely allowed by the courts to go into effect.

New York state is among a handful of states that eliminated the religious exemption to vaccine requirements for schoolchildren. The 2019 move came amid the nation’s worst measles outbreak in decades, with a majority of cases from outbreaks in New York in Orthodox Jewish communities.