De Blasio’s announcement marks one of the most aggressive steps taken by an elected official to combat a rise in Covid-19 cases caused by the Delta variant. In late July, the mayor mandated that unvaccinated city hospital workers and clinical staff at the city health department submit to a weekly Covid-19 test — a move first reported by POLITICO — and that city employment for new hires is contingent on vaccination.

An official described the move as just a first step toward a wider vaccine requirement in the nation’s biggest city.

“The mayor is now 100 percent [on board] and aggressively pushing vaccine certification,” said a City Hall official familiar with the discussions, who asked for anonymity to speak ahead of the formal announcement. “[De Blasio] wants it for everything indoors — public and private — but obviously has to scale implementation and expects a lot of pushback.”

The official added that New York City wants to “lead the nation in this regard.” The move is believed to be the first of its kind in the nation for a big city.

The policy comes as de Blasio has faced criticism for not reinstating mask-wearing mandates amid a recent spike in cases, but he has insisted the city’s focus has to be on vaccination. On Monday, Rep. Adriano Espaillat and City Council Member Mark Levine, who chairs the health committee, called for a similar proposal to the one being rolled out Tuesday.

Levine, a fellow Democrat, lauded the policy as “a critical move” and said it “will offer a powerful incentive for New Yorkers off the fence to get the vaccine.”

About 60 percent of all New Yorkers are partially vaccinated, though vaccination rates lag in Staten Island and Brooklyn, as well as among Black New Yorkers. Thirty-five percent of Black New Yorkers are partially vaccinated, compared with 76 percent of Asian, Native Hawaiian and Pacific Islanders, according to city data.

Council Member Joseph Borelli, a Republican who represents Staten Island, said vaccine hesitancy is broken down among racial and class lines, indicating that there are more factors to consider.

“It’s creating two classes of people,” he told POLITICO Tuesday. “It’s discriminatory in nature.”

The de Blasio administration said it has been in conversations with industry leaders to fortify the policy and proactively mitigate accusations of government overreach.

Equinox Group, which owns its eponymous, high-end gym chain, spin studio SoulCycle and Blink gyms, will adopt the policy in September, according to City Hall. Equinox informed its members of the policy change Monday, saying that “an overwhelming majority of members expressed support for requiring vaccines in order to access our Clubs,” according to an email sent from the gym’s president and the executive chair of the Equinox Group.

Union Square Hospitality Group CEO Danny Meyer, a restaurateur whose businesses include Gramercy Tavern and Shake Shack, was another early adopter of the policy.

The move also gained support from the New York City Hospitality Alliance, with some caveats.

“Mandating vaccine requirements for restaurant and bar employees and customers to work and dine indoors is a very difficult step for the industry, but ultimately may prove an essential move, to protecting public health and ensuring that New York City does not revert back to restrictions and shut down orders,” said Andrew Rigie, executive director of the trade group. “Any requirements need to include extensive outreach, education and support, and we stand ready to work with the city to keep workers and customers safe, while keeping restaurants, bars and clubs open with or without a vaccine requirement.”

De Blasio will sign a mayoral executive order in conjunction with City Health Commissioner Dave Chokshi releasing a commissioner’s order to put the policy into effect.