All New York City school staff will be required to take COVID-19 vaccines, according to a new mandate announced Monday by Mayor Bill de Blasio, Schools Chancellor Meisha Porter and Health Commissioner Dr. Dave Chokshi.

The mayor is expected to share further details at his daily press conference at 10 a.m. The mandate arrived Monday morning just as the U.S. Food and Drug Administration gave full approval to Pfizer-BioNTech's COVID-19 vaccine.

Unlike other city employees like hospital workers, Department of Education staff will not have an alternative to the vaccinations, such as weekly testing.

The policy will take effect September 27th and will require all department of education employees to upload proof of a first dose of vaccination to an online portal. Nearly one million public school students will return to school on September 13th.

"Our schools must be safe spaces for our students," Porter said Monday, calling the school staff vaccinations "another layer of protection for our kids."

Back in late July, the mayor called for all city employees to be vaccinated or undergo weekly COVID-19 testing by mid-September. Since then, city employee vaccinations have increased just four percentage points, with 58% having at least one dose as of early last week.

The city's announcement added that 63% of school staff have had at least one dose of COVID-19 vaccine so far.

De Blasio said on Monday that he would immediately start working with labor unions to address the mandate. Michael Mulgrew, president of the United Federation of Teachers, which represents 84,000 teachers and paraprofessionals, said in a statement: "Our first priority is keeping our kids safe, and the schools open.  The city’s teachers have led the way on this issue, with the great majority already vaccinated.  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."

When asked Monday afternoon on MSNBC if teachers would be fired for non-compliance under the new mandate, Mayor de Blasio replied his officials would be working "through the penalties" and that "there will clearly be consequences if someone doesn't comply." But he added the city's goal is to get people comfortable with vaccinations, and his team would be working with unions on the issue.

The mayor said he also felt confident that there would be sufficient "backup capacity" and "substitute teachers" in case a lot of teachers and other staff don't show up for work.

"I really think what's going to happen over these next weeks is that people are going to realize, especially with this FDA approval, that this is just the time to step forward," Mayor de Blasio told MSNBC's Aaron Gilchrist. "And we're confident that we'll have the staffing we need to run our schools well."

However, after a membership vote, the New York City Municipal Labor Committee will take legal action to require NYC to bargain the implementation of the vaccine policy. "

Many of the unions support and urge their members to be vaccinated. However, the City is required to collectively bargain the steps to be taken for implementing this policy” said Harry Nespoli, Chair of the Municipal Labor Committee, which represents 350,000 city employees. "Our members’ bargaining rights in this situation must be preserved. We are willing to discuss the steps for implementation as well as situations where accommodations would be appropriate."

Separately, New York City officials said the fact that the new mandate comes the same day as full FDA approval of the Pfizer vaccine was a coincidence and that they were planning to forge ahead even if the federal decision hadn't come today. New Jersey Governor Phil Murphy issued a vaccine-or-test requirement for public and private school teachers Monday afternoon, citing the FDA approval as part of his rationale.

Some parents are welcoming the news but wonder why this decision wasn't made earlier. That's because only full vaccinations--two doses of Pfizer and Moderna or the single shot from Johnson & Johnson--are thought to thwart the delta variant. The Department of Education, meanwhile, is asking only for proof of one dose.

Karin Venegas, an Astoria resident whose daughter will start kindergarten next month, said the city should have implemented a mandate with more lead time ahead of the first day of school, "at least for schools serving children under the age of 12."

The Pfizer and Moderna vaccines require three to four weeks between their two doses and another 14 days to take full effect. So even if a teacher received their first doses of these vaccines today, they wouldn't be fully inoculated by the start of the school year on September 13th. (Last week, the city Health Department told WNYC/Gothamist that 95% of New Yorkers are still following up on their second shots.) The Johnson & Johnson COVID-19 vaccine is fully effective 14 days after its single shot.

The city has repeatedly asserted that there will be no remote learning in the upcoming school year. When asked about the possibility of remote options last week, de Blasio said, "I am absolutely convinced that with all the health and safety measures put in place, and a lot more vaccination that is going to happen between now and the opening day of school, with kids and with adults in the school system, this is going to be the place that the kids need to be."