Go out for a night on the town in some U.S. cities and you might find yourself waiting while someone at the door of the restaurant or theater closely inspects your vaccination card and checks it against your photo ID. Or, conversely, you might be waved right through just by flashing your card.

How rigorously vaccination requirements are being enforced varies from place to place, even within the same state or city.

Proof of vaccination is required in several American cities to get into restaurants and bars, enjoy a concert or a play, catch a movie or go to a ballgame.

Ticket agents dutifully ascertain the vaccination status of everyone passing through the turnstile at pro sports venues in some cities from Seattle and New York, and restaurant hosts do the same in many places. In other locations, vaccine checks are cursory at best. Sometimes it’s practically done on the honor system.

“There are some businesses that say they check for vaccination proof, but they are not even checking,” said Jay Matsler, of Palm Springs, California, who was visiting San Francisco’s Fisherman’s Wharf with his partner Monday during a stop of their cruise along the California coast.

“We actually tell them, ‘I’m sorry, you’re not enforcing this. We’re not going to give you our business,’” Matsler said. He said they were recently in Prague and Paris and had to show their vaccination cards and IDs at every indoor space they visited.

Some places around the U.S. are afraid of losing business if they insist on proof. Some say they don’t have enough staff to conduct such checks amid a nationwide labor shortage. Some object on principle.

And some don’t want to risk ugly confrontations. At an Italian restaurant in New York City, a request that a group of customers show vaccination proof led to a brawl.

During the first month of enforcement in New York, inspectors issued warnings to 6,000 businesses for not checking patrons’ status, and 15 were fined $1,000 for being repeat offenders. The indoor dining area at an In-N-Out Burger joint in San Francisco was shut down this month by health authorities for not demanding proof of vaccination.

Public health authorities see the requirements as vital tools in slowing COVID-19 at a time when 1,500 or more Americans are dying each day from the virus. Such rules face deep opposition in conservative states, meaning they are mainly in effect in Democratic-run locations.

At the Highway Inn restaurant in Honolulu on Monday, the hostess asked diners for proof of vaccination or a negative test before seating them indoors. The information on their cards must match their IDs, and they must also give contact information that the restaurant keeps on record for two weeks in case of an outbreak.

Russell Ryan, the restaurant’s co-owner, said business declined when the vaccine requirement for restaurants first went into effect in mid-September. A few unvaccinated people “stormed off in a huff,” he said, but most have complied, and business has returned as more people have gotten vaccinated.

“Generally, it has been less confrontational than we feared,” Ryan said. “We thought that we’d get some zealots who want to make a stand for whatever reason.”

In many places in the U.S., precisely how to enforce the vaccination rule is left up to businesses.

At a movie theater on a recent night in San Francisco, teenagers at the concession stand glanced at patrons’ cellphone photos of their vaccination cards before handing them their popcorn, candy and drinks.

At the city’s Opera House, however, an usher closely examines the proof of vaccination and compares it against a picture ID. Anyone who fails to show proof will be asked to leave.

San Francisco health inspectors checking on the food permits of restaurants also routinely look to see whether businesses are complying with the proof-of-vaccination rules, but the city relies largely on complaints of violations phoned in to its 311 line.

Since the city’s mandate went into effect on Aug. 20, only one restaurant has been penalized — the In-N-Out at Fisherman’s Wharf that was closed for the day on Oct. 14 after refusing to ask for proof of vaccination despite several warnings from the city. The burger place now serves only takeout. A spokesman said the company refuses to be “the vaccination police for any government.”

In Los Angeles County, health inspectors found 38 venues that needed more training on vaccine rules out of about 250 bars, lounges, nightclubs, breweries, wineries and distilleries checked between Oct. 8 and Oct. 17. When the county visited 78 bars the next week, they found about 15% of them weren’t in compliance with customer vaccine verification rules, triggering more training.

New Orleans is also among the big cities that have imposed such rules, and Los Angeles plans to roll out its own requirements next week.

In New York City, big venues, like Broadway theaters and museums, tend to enforce the rules strictly. A neighborhood cafe might not.

“The vast, vast, vast majority of restaurants and all the other businesses are saying, ‘Yes, we’re going to work with this. We’re going to make it work for our employees, for our customers, keep everyone safe,’” Mayor Bill de Blasio said.

Some business owners around the U.S. have opted to close their dining rooms and offer only takeout or outdoor seating.

In Honolulu, hostess Ku’uipo Lorenzo greeted customers Ashley and Martin Day as they arrived at the Highway Inn for authentic Hawaiian food. They were seated at a table after Ashley produced her vaccine card and her unvaccinated husband showed a recent negative COVID-19 test.

“We have different perspectives,” Ashley Day said. “I think we both agree that it should probably be a testing mandate rather than a vaccine mandate.”

But the Days look forward to when tests and vaccines aren’t needed to dine out.

“I think we’d like to see things open up again,” said Ashley.