The city’s largest municipal labor union launched a full-court press on Wednesday against Mayor de Blasio’s order to return to work, a day after a state Supreme Court granted it and other unions a temporary restraining order on the implementation of city vaccine mandates.

Henry Garrido, the executive director of DC37, announced Wednesday that the union filed an “improper practice petition” with the city’s Office of Collective Bargaining over de Blasio’s requirement that all city employees return to their offices after working remotely for months — or face the possibility of punishment.

“The workers who make up District Council 37 have kept New York City running for the last 18 months. They’ve proven time and again that no matter where they are, the job will get done,” Garrido said in a written statement. “With the delta variant and all the others, the landscape of COVID-19 is too uncertain to needlessly force people back to their desks. We will not let our members be used as guinea pigs.”

Garrido said he filed the petition with the Office of Collective Bargaining because the city should allow nonessential workers to work from home “until we are certain it’s safe.”

Five days earlier in a Daily News op-ed, he argued that to implement his policy de Blasio’s Department of Citywide Administrative Services went so far as to remove “the social distancing requirement still recommended by the federal Centers for Disease Control and Prevention.”

De Blasio disputed that Wednesday and responded that the city is “following appropriate health and safety standards.”

Wednesday’s broadside from Garrido, an ally of the mayor for years, also came a day after a Manhattan Supreme Court justice issued a temporary restraining order blocking the city from moving forward with its mandate that all public school staff be vaccinated.

That order from Justice Laurence Love is only set to remain in effect until Sept. 22, five days before the deadline school employees have to get vaccinated under de Blasio’s directive.

Garrido, whose union was among several others that requested the court intervene, interpreted the restraining order as support from the court.

“While we do believe our members should get the vaccine, we do not believe it should be a condition of employment,” he said Tuesday evening. “Clearly, the courts agree.”

De Blasio did not seem fazed, though.

The restraining order is temporary, and Hizzoner said he’s confident the city will ultimately prevail when it comes to mandating its workers be vaccinated, citing the fact that the city’s order comes amid a pandemic and with tacit approval from President Biden, who recently issued vaccine rules for large companies.

“We’re employers. We have a right to keep our workforce safe and healthy,” he said. “We feel all those factors make very clear the correctness of our position.”

He also pushed back against the petition Garrido filed hours earlier and reiterated his claim that city workers are more productive when they’re not working remotely.

“Public servants do their best work when they’re in person at their offices,” he said. “It’s time. It’s time for people to be back at their offices doing the jobs they were hired to do.”