A federal appeals court has lifted an order blocking New York City from enforcing a vaccine mandate for public school staff.

The ruling came Monday night, when the mandate originally had been scheduled to take effect.

Shortly after the judges’ ruling, Mayor de Blasio said on NY1’s Inside City Hall that all public school staff must now get their first shot of the COVID-19 vaccine by the end of the workday Friday, meaning the mandate would go into effect when the new work week begins on Monday, October 4th.

"If you have not gotten that first dose by Friday five o’clock, we will assume you are not coming to work on Monday and you will not be paid starting Monday and we will fill your role with a substitute or an alternative employee," he said.

The legal wrangling has been whiplash inducing.

Earlier this month, a coalition of municipal unions sued the city saying the mandate violates due process. A state supreme court judge issued a temporary restraining order, then lifted it last week. He is supposed to issue a final decision any day, but has indicated that a century of case law and the benefit to public health support the mandate.

A group of teachers and paraprofessionals also sued the city in federal court, prompting the injunction that was subsequently lifted Monday night.

A third group of educators has also filed a lawsuit challenging the mandate.

As of Monday, officials said 87 percent of school employees have gotten at least one dose, and 90 percent of teachers. But that still leaves thousands of staff members who have not, and some principals have warned of a staffing shortage. More than 500 educators have received medical and religious exemptions. Employees who get permission to forego the vaccine are being transferred to roles outside school settings. Staff who don’t qualify for those exemptions either have to take unpaid leave with health insurance or resign.

"The courts have cleared the way for the city to begin enforcing the city’s vaccine mandate for school employees,” said Michael Mulgrew, president of the United Federation of Teachers. “The city has a lot of work before it to ensure that enough vaccinated staff will be available by the new deadline.”