(Bloomberg) -- New York City’s school system, the largest in the U.S., has been temporarily blocked from imposing a mandate forcing teachers and other staff from getting vaccinated against Covid-19, according to a ruling from a federal judge. 

That mandate is scheduled to go into effect on Monday at midnight. 

Late Friday, a judge from the U.S. Court of Appeals for the Second Circuit referred the case to a three-judge panel “on an expedited basis.” It was unclear if that hearing will take place before Monday. 

The presidents of the city’s teachers and principals unions this week urged Mayor Bill de Blasio to push back the vaccination deadline, warning it will result in employee shortages that will imperil the safety of children. The mayor refused to do so.

“We’re confident our vaccine mandate will continue to be upheld once all the facts have been presented, because that is the level of protection our students and staff deserve,” Department of Education spokesperson Danielle Filson said in a statement. 

She said that more than 82% of the department’s employees had been vaccinated, “and we continue to urge all employees to get their shot by September 27.”

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