LOS ANGELES — People entering a wide variety of businesses in the city of Los Angeles began having to show proof of COVID-19 vaccination on Monday as one of the country’s strictest measures intended to slow spread of the coronavirus took effect.

The new rule covers businesses ranging from restaurants to shopping malls and theaters to nail and hair salons

At Blue Bottle Coffee in the Los Feliz neighborhood, a sign on the front door reminds patrons that they must show proof of vaccination if they want to eat indoors.

Manager Matthew Cadena said the morning rush was mostly smooth as customers handed over their vaccine cards or showed photos of them on their cellphones. Some patrons had put an image of their vaccine card on their phones’ home screen.

“Most people are accommodating and understanding,” Cadena said.

Only a handful of people saw the mandate as “nonsensical,” Cadena said, and they were directed to outdoor tables with a to-go order if they did not show vaccine proof.

Los Angeles is among a growing number of cities across the U.S., including San Francisco and New York City, requiring people show proof of vaccination to enter various types of businesses and venues. But rules in the nation’s second-most-populous city, called SafePassLA, apply to more types of businesses and other indoor locations including museums and convention centers.

They are being implemented as new cases have started inching up following a sharp decline from an August peak driven by the delta variant.

This was the time of year in 2020 when the worst spike of the pandemic was just beginning in California, which by January saw an average of 500 people die every day. Los Angeles became the state’s epicenter and its hospitals were so overloaded with patients that ambulances idled outside with people struggling to breathe, waiting for beds to open.

So many people died that morgues reached capacity and refrigerated trucks were brought in to handle the overflow. That stark scene played out as coronavirus vaccines arrived and California and Los Angeles moved aggressively to inoculate people.

Among LA county’s roughly 10 million people, 80% of eligible residents now have received at least one COVID-19 vaccine dose and 71% of those eligible are fully vaccinated, according to public health officials.

To guard against anything resembling the January carnage, the LA City Council voted 11-2 last month for the ordinance that requires people 12 and older to be fully vaccinated to enter indoor public spaces including sports arenas, museums, spas, indoor city facilities and other locations.

Negative coronavirus tests within 72 hours of entry to those establishments would be required for people with religious or medical exemptions for vaccinations. Customers without proof can still use outdoor facilities and can briefly enter a business to use a restroom or pick up a food order.

While the order took effect Monday, city officials say they won’t start enforcing it until Nov. 29 to give businesses time to adjust. A first offense will bring a warning but subsequent ones could produce fines running from $1,000 to $5,000.

Los Angeles Mayor Eric Garcetti, who tested positive for the coronavirus last week while attending the United Nations climate change conference in Scotland, said the mandate will encourage more people to get shots and make businesses safer for employees and customers.

“Vaccinating more Angelenos is our only way out of this pandemic, and we must do everything in our power to keep pushing those numbers up,” Garcetti said.

Business trade groups say the mandate will sow confusion because Los Angeles County’s own vaccine rules — which apply to dozens of surrounding communities — are less sweeping. Cities are allowed to pass rules more stringent than the county’s.

“There’s a tremendous lack of clarity,” said Sarah Wiltfong, senior policy manager at the Los Angeles County Business Federation. For example, most retail shops are exempt. “But shopping malls and shopping centers are included, which of course includes retail shops,” she said.

Harassment of workers who are tasked with verifying vaccination is the top concern of the business federation’s members, Wiltfong said.

“This puts employees in a potential position of conflict, when they’re not necessarily trained to handle situations like that,” she said.

In interviews last week, yoga studio owner David Gross said he felt relief in knowing he and his co-owner wouldn’t have to unilaterally decide whether to verify their customers are vaccinated, while in another part of town, the manager of a struggling nail salon felt trepidation and expected to lose customers. “This is going to be hard for us,” Lucila Vazquez said.

Salons were especially hard hit during the pandemic and were among the last businesses to reopen indoors. Before the pandemic, Lynda Nail Salon in the Los Feliz neighborhood was regularly filled with clients for hair and nail appointments. On Wednesday morning, only one woman waited for her hair to set.

Vazquez, who manages the business, said she will follow the new rules even though many of her hair clients have said they won’t come in if it requires being vaccinated.

Gyms and yoga studio like the one co-owned by Gross also fall under the order. He doesn’t relish having his employees play the role of enforcer, checking every customer’s vaccination status. But now that the rule is on the books, it’s one less decision he and his partner Lydia Stone have to make as they navigate Highland Park Yoga back to in-person classes.

In anticipation of the new rules, the studio last month started encouraging its regular customers to submit their vaccine cards online so they don’t have to show them at the start of every class. Gross and Stone said it would be heartbreaking to turn away anyone.

“You know, the City Council decided, the mayor signed it, and we we have no choice but to comply with the law,” Gross said, adding that the possibility of being punished for violating the law “would be hugely detrimental” to a yoga business that is barely surviving after being shut down for the bulk of the pandemic.