Mayor de Blasio is expected on Monday to announce how the city will respond to the Centers for Disease Control’s updated recommendation that vaccinated people now wear masks indoors.
He said last week the city's health team was reviewing the advisory.
Other parts of the country have reinstated mask mandates, including Nevada.
The state’s order went into effect this weekend and applies to everyone, vaccinated or not.
Casinos on the strip are now required to post signs notifying visitors of the mask rules.
Washington D.C. has also reinstated its mask mandate as COVID-19 cases increased five fold in July.
Some businesses there are also adding their own safety measures, including many bars and restaurants, which are now requiring proof of vaccination before entering.
New York City restaurateur Danny Meyer implemented such a policy last week at his eateries.
De Blasio hinted on Friday that a vaccine mandate could be coming to all city restaurants.