Starting Monday, New York City will be the first major US city to introduce vaccination requirements for indoor dining, creating a host of new challenges for restaurant operators in the five boroughs.

Due to the surge in new Covid-19 cases related to the Delta variant, the city requires proof of at least one vaccine dose for a number of indoor activities, including restaurants, health clubs and attending indoor performances in New York City the first US major city that imposes such restrictions. Employees of these facilities must also be vaccinated. After a few weeks until the transition, enforcement is scheduled to begin on September 13th.

Politics is gaining momentum. On Thursday, San Francisco followed New York’s lead in introducing its own mandatory vaccination for indoor activities, which will go into effect on August 20, checking the status of its workers. Los Angeles is considering a similar plan.

As more and more vaccination regulations come from places and the restaurants themselves, Booking Holdings’ OpenTable has introduced a feature that allows restaurants to display their Covid vaccination requirements to their customers. The reservations service also plans to publish a national list of restaurants that require proof of vaccination.

The New York mandate is bound to have a learning curve. But restaurants are also waiting for more detailed instructions from city officials on how much information to collect and record from customers.

“I feel like it’s going to be a little bit free on Monday where customers and restaurants don’t really know what’s going on with it,” said Art Depole, the co-owner of a Mooyah Burger, Fries, and Shakes franchise with brother Nick in Midtown Manhattan .

Chipotle Mexican Grill CEO Brian Niccol told the Washington Post on Wednesday that the city should figure out how vaccination requirements apply to people who cannot be vaccinated for medical or religious reasons. Otherwise, they will be excluded from the workforce.

Workers are an ongoing challenge for industry that needs all the workforce it can get. Restaurants have raised wages and offered retention bonuses to attract new workers, but the unemployment rate for restaurants and bars was still 8.4% nationwide in July, according to the Bureau of Labor Statistics.

Depole said more than half of its Mooyah employees are vaccinated. However, he sees vocal opposition from a handful of his unvaccinated workers who threaten to resign if vaccination becomes a job term. The enforcement of mandates also puts a strain on his employees, who would have to deal with non-compliant customers.

And the verification of vaccination records could also mean adding an extra worker to stand at the door for the entire shift, adding to the restaurants’ rising labor costs. Chipotle is still trying to figure out how it’ll verify vaccination records.

“Of course it’s something that takes some thought if we want it to be really workable,” said Niccol.

Tourists present another difficulty in fulfilling the mandate. Depole’s Mooyah restaurant is located between Times Square and Herald Square, two tourist hotspots, and orders from these customers are required.

“It seems like there are more locals on board and understand, but the tourists and the non-residents say, ‘Oh no, this is the last time you will see me in town,'” said Depole. “It’s a polarizing topic.”

And while the number of international tourists is unlikely to return to pre-pandemic levels until 2025, some are still traveling to New York City. For visitors from outside the United States, some may have difficulty getting their vaccination card recognized.

For example, retail advisor and founder of SW Retail Advisors Stacey Widlitz received the Oxford-AstraZeneca vaccine in the UK. While the World Health Organization approved the vaccine, Widlitz struggled to get some New York companies to accept their proof of vaccination: a QR code generated by the National Health Service’s mobile app.

“I’m not a tourist, but I had my vaccine in London and they don’t know what to do with a barcode from a foreign country in an app they don’t know,” said Widlitz. “They give you a blank look.”

So far, a gym in the Upper East Side Widlitz has already announced that it would only accept the vaccines Moderna, Pfizer or Johnson & Johnson if she wanted to train without a mask. Workers at several independent restaurants told her that after the mandate went into effect, they would no longer be able to eat indoors because they would not have a way to check vaccinations that were held outside of the United States.

However, restaurant operators will also see some benefits from the vaccine mandate, besides containing the tide of new Covid cases. For one, it could limit the number of workers who call in sick because they tested positive or came in contact with someone who did so. Niccol, for example, told the Washington Post that more workers are missing shifts in the burrito chain due to the Delta variant, although the burrito chain will not implement a company-wide vaccine mandate until the vaccines receive final regulatory approval.

The mandate could also encourage some consumers who were hesitant to return to restaurants to dine indoors again. Le Bernadin’s chef Eric Ripert said Thursday on CNBC’s Worldwide Exchange that his restaurant’s existing vaccination policy has made customers easier and safer rather than alienating them.

“There is a very big difference between what we see on social media and the reality of what happens to the business,” he said.