New York City schools are bracing for a massive staff shortage as tens of thousands of educators and other school personnel resist a COVID-19 vaccine mandate that is set to take effect on Tuesday, September 28th.

According to Chalkbeat, 10,000 teachers – about 13% of the citywide total – have yet to provide proof that they’ve been inoculated. Nearly 20,000 other education department employees, including cafeteria workers and security guards, also lack proof of vaccination. They have until the end of the day Monday to provide documentation or go on unpaid leave starting Tuesday.

Mayor Bill de Blasio says 11,000 substitute teachers are ready to fill any gaps, but unions are urging him to push back the deadline to give educators more time to comply.

“It is dangerous and irresponsible for the city to move forward with its plan to allow schools and centers to operate so severely understaffed. As a result, we are calling on the city to delay the deadline for the mandate to allow the city to develop a reasonable contingency plan,” said CSA President Mark Cannizzaro in a statement Thursday.

Chalkbeat adds:

Even if the city is able to find subs to fill in for unvaccinated employees, Cannizzaro said young students need consistent relationships with teachers, and older students need educators with expertise to help them catch up after more than a year of interrupted learning.

“I believe that the mayor thinks that a body is a body — get them in, and we’re good,” Cannizzaro said. “That’s no way to run a school.”

Pediatric cases of COVID-19 have been on the rise as students have returned to in-person learning. In the four weeks preceding September 16th, 925,000 children were infected with the virus, according to The American Academy of Pediatrics. Pediatric COVID-19 case have soared by 240% since early July.

School employees have had ample time to get vaccinated. They were given early access to the jabs when they first emerged, and NYC’s mandate has been on the books for over a month. Legal challenges to the mandate have thus far failed, but a major decision is expected next week.

de Blasio said staff from the city’s Department of Education headquarters will be deployed to schools to help combat the shortages. He’s also authorized funding for schools to hire “regular substitutes” for the duration of the year.

At a press conference on Thursday, de Blasio said he expects more school staff will get vaccinated in the coming days. “In short order, they’re not going to be getting a paycheck” he said.

School staff shortages have become a nationwide problem. The Associated Press reports:

One desperate California school district is sending flyers home in students’ lunchboxes, telling parents it’s “now hiring.” Elsewhere, principals are filling in as crossing guards, teachers are being offered signing bonuses and schools are moving back to online learning.