(AP) — San Francisco became the first major city in the nation to require proof of full vaccination against COVID-19 on Friday for people dining inside restaurants, working out in gyms or attending indoor concerts.

Restaurants and bars posted signs and added extra staff to begin verifying people’s proof of vaccination before allowing them in.

“There’s definitely some anxiety around how it’s all going to work,” said Pete Sittnick, a managing partner of Waterbar and EPIC Steak restaurants on the city’s waterfront.

He anticipates a slowdown in checking in diners, possible pushback from guests who disagree with the requirement and awkward scenarios where someone shows up without proper documentation.

“The good thing is, if somebody doesn’t have their verification of vaccination they can still eat outside. There is an option and we just need to be ready for different scenarios,” he said.

Mayor London Breed announced the requirement more than a week ago in an attempt to stem rising COVID-19 cases, saying she was worried the highly contagious delta variant of the coronavirus could disrupt the city’s economic rebound.

The mandate goes further than New York City, which requires people to be at least partially inoculated for a variety of high-risk indoor activities, and New Orleans, which requires proof of vaccination or a negative COVID-19 test for indoor dining or drinking.

It follows a number of tough COVID-19 measures San Francisco imposed since the beginning of the pandemic. The city and its neighboring counties in the Bay Area were the first in the nation to order residents to stay at home in order to slow the spread of the coronavirus, and was the first big city in the nation to require all city employees to be vaccinated, without the option of testing regularly.

The majority of 36,000 city workers said they are vaccinated, but about 4,300 have not. This week, the city sent letters recommending a 10-day suspension without pay for 20 employees in police, fire and sheriff’s departments who refused to report their vaccination status by the Aug. 12 deadline, the San Francisco Chronicle reported.

Gov. Gavin Newsom has also had to tighten the rules after announcing the reopening of California’s economy in June. He has required the state’s health care workers to get vaccinated to keep their jobs and all teachers and state workers to either get vaccinated or submit to weekly testing.

Local business groups have supported the new vaccine mandate, saying it will protect their employees’ and customers’ health and keep them from having to limit capacity indoors. Some businesses that had taken it upon themselves to check for proof of vaccination at the door said a citywide policy helps set clear expectations for all customers.

When Vegan Picnic announced in late July it would only allow vaccinated customers, the deli quickly received one-star reviews on Yelp, many from internet trolls who had never eaten there, and threats from callers who viewed the requirement as a violation of their personal rights and privacy, owner Jill Ritchie said.

“The phone was ringing with people yelling at us, and at the same time we had an outpouring of support from people saying ‘Thank you, I feel safe going to your store,'” Ritchie said.

She said checking people’s vaccination status has been easy, and soon the computer software her business uses for online ordering and payment processing will handle the verification digitally and warn customers of the mandate ahead of time.

Online reservation systems such as OpenTable are also telling diners about the rule when they RSVP, and businesses that cater to the city’s tourism industry launched a campaign called “Relax, We’re Vaxxed” to get the word out to out-of-town visitors.

City officials said a paper card issued by the U.S. Centers for Disease Control and Prevention, a photo of the CDC card, or a verified digital vaccine record will suffice. Proof of vaccination issued by foreign governments is also acceptable.

Pearce Cleaveland, co-owner of the Temple nightclub, said his security guards have been trained to check all forms of vaccination proof and they have caught some people with falsified copies of vaccination cards.

“We’ve had people who get upset at the door when they’re turned away, but in general they’re understanding,” he said. “It’s the tourists who are generally disappointed, when they’re unaware of the requirement and can’t get vaccinated quickly enough.”

Workers have until Oct. 13 to prove they are fully vaccinated and Cleaveland said he expects to meet compliance by then. The mandate does not apply to people ineligible for vaccines, including children under 12.

After a sharp increase in coronavirus cases and hospitalizations in the San Francisco Bay Area over the summer, the numbers appear to be leveling off but remain high, said Dr. Peter Chin-Hong, an expert on infectious diseases at the University of California, San Francisco.

He said reinstated restrictions have helped slow the spread of the coronavirus. For example, after Los Angeles County reinstated a mask mandate for indoor businesses, the increase in daily COVID-19 cases slowed significantly over the last few weeks, Chin-Hong said.

“There is no magic bullet, just a combination of a hard stick and soft stick,” he said. “The proof of vaccination mandate is a soft stick because you can still eat outdoors, but if you want to hang out with people indoors you better get vaccinated.”