New York City is imposing a vaccine mandate for all private sector employers as a preemptive measure to fight a surge of Covid cases this winter, Mayor Bill de Blasio announced on Monday.

The mandate will go into effect on Dec. 27, de Blasio said.

“We’ve got omicron as a new factor, we’ve got the colder weather, which is really going to create additional challenges with the delta variant, we’ve got holiday gatherings,” de Blasio told MSNBC Monday morning. “We in New York City have decided to use a preemptive strike to really do something bold to stop the further growth of Covid and the dangers it’s causing to all of us.”