Proof of vaccination against COVID-19 will be required for staff and customers of indoor venues in the city starting Monday.

Mayor Bill de Blasio announced the mandate last week as part of his Key to NYC plan. The mandate will go into effect on Monday and be fully enforced on Sept. 13.

The mandate means workers and customers of indoor dining, indoor fitness and indoor entertainment venues must show proof of vaccination against COVID-19 through their vaccine cards, the NYC COVID Safe app or the NYS Excelsior app.

This comes after the Barclays Center announced that all employees and guests ages 12 and over must show proof of vaccination starting Sept. 13.  The mayor said on Twitter that the Barclays Center's announcement “will keep the best basketball fans in the world safe.”

The citywide mandate will be the first-in-the-nation vaccine requirement for employees and customers for indoor venues.

While the mandate doesn’t go into effect until Monday, de Blasio says over 50 businesses in the city have already started to require proof of vaccination for entry. The mayor called these businesses “early adopters” and applauded them for already following the new protocols.

So far, 56% of New York City residents are fully vaccinated against COVID-19. There have been over 1,300 confirmed cases in the city in the last week.