New York City is requiring all 148,000 public school teachers and employees to be vaccinated against Covid-19 this fall, expanding a mandate already in place for city and health care workers.

Public school staff in New York City’s five boroughs must be given at least one dose of Covid vaccine by September 27, city officials said at a news conference Monday morning. The mandate does not allow school staff to submit negative Covid test results instead of getting vaccinated, the city’s Department of Education confirmed to CNBC.

“The Covid-19 vaccination for teachers and other staff as well as all eligible students is an important strategy to get us back to school,” said Dr. Dave Chokshi, the city’s health commissioner, at the meeting. “And today’s announcement that the FDA has given Pfizer vaccine full approval adds to the crescendo of evidence that Covid-19 vaccines are both safe and effective.”

New York City’s public school system is the largest in the country, with nearly 1.1 million students in nearly 1,900 schools. The mandate covers all employees in the education sector, including teachers, school principals, caretakers, catering staff and security personnel.

New York City Mayor Bill de Blasio said he plans to further discuss the mandate with the city’s teacher unions. His comments came less than two weeks after Randi Weingarten, president of the American Federation of Teachers, told CNBC she supported a vaccine mandate for educators to protect against the emerging Delta variant.

“All parties are clearly ready to sit down at the negotiating table and find out what this means and what impact this has in order to see together whether we can solve the outstanding problems,” said de Blasio.

According to the White House, around 90 percent of teachers nationwide are vaccinated against the coronavirus. City Schools Chancellor Meisha Ross Porter said at the meeting that at least 63% of all Department of Education staff are also vaccinated.

De Blasio has also prescribed vaccines for select activities across the city. Customers and employees of the city’s indoor restaurants, gyms and entertainment centers must demonstrate by September 13th that they have received at least one dose of vaccine.

Other states, such as California, have introduced softer mandates for school staff that require mandatory testing for teachers and staff who are not vaccinated. New Jersey Governor Phil Murphy announced a similar protocol on Monday that would require all staff from kindergarten through 12th grade to be fully vaccinated for Covid or tested at least once a week.