The Kroger supermarket in Yorktown, Virginia, is in a county where mask-wearing can be casual at best. Yet for months, the store urged patrons to cover their noses and mouths, and almost everyone complied.

“People don’t like to wear masks here,” said Janet Wainwright, a meat cutter at the store, “but very few people would go without it.”

That changed in mid-May after the Centers for Disease Control and Prevention advised vaccinated Americans that they could go maskless in most indoor settings. The next week, the store told employees that they could no longer ask customers to cover their faces. So mask use plummeted, and the anxiety of Wainwright and other workers shot up.

“We just feel like we’re sitting ducks,” said Wainwright, who estimated that far fewer than half of patrons wore masks on a recent Sunday. “Now it’s just a free-for-all.”

More than a dozen retail, hospitality and fast-food workers across the country interviewed by The New York Times expressed alarm that their employers had used the CDC guidance to make masks optional for vaccinated customers. Some, including Wainwright, said they had been vaccinated but worried they could still get sick or infect family members who were not or could not get vaccinated. Others said they had yet to be vaccinated.

Public health experts say people who are fully vaccinated have a very low risk of developing serious illness from COVID-19. Vaccinated people are also less likely to transmit the virus to others. Overall cases have fallen substantially in recent weeks, and vaccines are widely available.

Kroger, like all the employers contacted for this article, pointed to the new CDC guidance in explaining the change in masking policy. The CDC did not respond to a request for comment.

The effect of the change appears to be most acute in politically mixed or conservative areas, where many people have chafed at mask requirements and vaccination rates are lower. In liberal enclaves, where public support for masking has generally been high, many customers continue to wear masks whether they are required.

In mixed and conservative areas, workers said, employer policies were often the only thing standing between them and customers who were neither masked nor vaccinated. As a result, they feel far more exposed now.

“Retailers were asking and requiring you to wear masks,” said Willy Solis, a shopper for the delivery app Shipt in Denton, Texas, who works in stores including Target, Kroger and CVS. “A large majority of people were still doing the right thing and wearing them.”

Since the CDC announcement, however, “it’s been a complete shift,” Solis said. Denton, like Yorktown, sits in a county that supported former President Donald Trump by a single-digit margin in the November election.

According to the Kaiser Family Foundation, 97% of Democrats said in a March poll that they wore a mask “at least most of the time” when they might be in contact with people outside their homes, and a similar portion of Democrats said they believed masks limit the spread of the coronavirus.

That compared with only 71% of Republicans who said they wore a mask outside the home at least most of the time, and just half said they thought masks were effective.

That suggests that a significant number of Republicans have worn masks only to comply with rules, not because they believed it was important, said Ashley Kirzinger, the Kaiser foundation’s associate director for public opinion and survey research. She cited polling showing that Republicans were also less likely to be vaccinated.

Matt Kennon, a room service server at the Beau Rivage Resort and Casino in Biloxi, Mississippi, said that before the CDC relaxed its recommendations, the resort’s policy was that all guests must wear masks in common areas unless they were eating, drinking or smoking, and that it was strictly enforced.

“There were several security checkpoints around the place where we’d have someone from security let them know, ‘Please put on a mask,’” said Kennon, a shop steward with his union, UNITE HERE. “There were stations with disposable masks for guests to wear in case they didn’t have one.”

Kennon said the policy remained in place even after the governor lifted a statewide mask mandate in early March but changed after the CDC announcement. Vaccinated guests are allowed to walk around without masks, but there is no way to verify vaccination status and fewer than half of guests are wearing them, according to Kennon.

“Security won’t ask them to show a vaccine card,” he said. “It’s certainly stressful amongst my co-workers.”

By contrast, in Bethesda, Maryland, in a county where the majority voted for President Joe Biden, mask-wearing appears to be largely unaffected by the CDC shift.

Linda Bussey, a merchandise manager in the health, beauty and care department of a Safeway there, said her store put signs up May 21 indicating that vaccinated customers could enter without wearing a mask and instructed employees not to approach maskless customers, but that the rate of mask-wearing appeared unchanged.

The experience of employees at REI, the outdoor equipment retailer, reflects the experience of many workers across the country. While many REI stores are in or near liberal communities, they often abut more rural areas, leading to frequent interactions between employees and more conservative customers.

“If you go two minutes in any direction, it’s a blood-red state,” said Mike Mason, an employee at an REI store in Bellingham, Washington. “It’s a weird mix of two different personalities.”

Mason, along with REI employees in five other states, said the company had previously been strict about its mask policy, with many stores employing a greeter to remind customers.

But REI shifted its policy within 24 hours of the CDC announcement, telling stores that they “do not need to enforce mask policies with either employees or customers who may no longer wish to wear one,” according to an internal message from a top executive.

The next week, the retailer announced that it would not require vaccinated customers to wear face coverings where allowed by local authorities and instructed employees to assume that patrons were following the policy in good faith.

Mason, along with employees of REI stores near Salt Lake City, Des Moines, Iowa, and Columbus, Ohio, said the percentage of customers wearing masks had dropped significantly after the change. The timing was an additional source of stress because the retailer began its annual anniversary sale a few days later — typically one of its busiest periods of the year.

“We had people walking in, not buying anything, just chewing gum with their mouths open — a ‘see if anyone stops me’ kind of dance,’” said Mason, who is vaccinated but worries about infecting his toddler and the baby he and his wife are expecting. “I’m already taking prescription meds for anxiety. I had to increase my dosage to keep my heart from racing.”

At an REI store in Portland, Oregon, several employees walked off the job after the new policy was announced. Later that day, REI reversed itself and announced that stores in Oregon would maintain their masking requirement at least until the annual sale ended.

“The fact that they announced it out of the blue with no guidance, nothing,” said Brian Levitt Smith, one of the employees who left work, “it was kind of shocking.”

David Michaels, a former head of the Occupational Safety and Health Administration, said the patchwork of responses from employers highlighted the importance of a set of federal workplace rules, known as a standard, that the government could enforce.

“This underscores the need for a standard right now,” said Michaels, now at the George Washington University School of Public Health. “Many employers are following state guidance, which is throwing public health precautions out the window.”

Wainwright, who serves as a shop steward for her local United Food and Commercial Workers union, said she and her colleagues were scarred by what they had seen during the pandemic. Several of her co-workers at Kroger in Yorktown contracted the virus, and one woman died last spring. A man in his 20s who was not vaccinated was out sick for weeks this spring.

Kroger did not respond to questions about workers who became ill.

“Everyone is scared,” Wainwright said. “We have had so much COVID anyway, and that was with a mask mandate. Without the mask mandate, we have a fear of the unknown.”