Starbucks ends its plan to require worker vaccination and testing.

The Supreme Court’s ruling last week shutting down the Biden administration’s effort to enlist large employers in its vaccination campaign, experts said, would trigger a new wave of uncertainty about how companies keep workers safe from Covid-19.

Now Starbucks, with 9,000 U.S. coffee shops and 200,000 workers, has became one of the first major retailers to backtrack on its vaccine plans since the ruling.

Starbucks told its employees in a memo on Tuesday that they would no longer be required to be fully vaccinated or submit to weekly coronavirus testing. Just two weeks earlier, the company had detailed the requirement and set a deadline of Feb. 9.

The Supreme Court’s decision did not prohibit companies from keeping their vaccine rules in place, and many will continue rolling out stringent Covid-19 safety protocols, especially as Covid case counts remain high.

Starbucks’s move to drop its vaccine-or-test deadline highlights how the court’s ruling has put the responsibility for determining vaccination rules squarely on employers. And companies face a patchwork of federal, state and local laws, which range from vaccine mandates that are stricter than the federal government’s to laws blocking companies from requiring workers to wear masks.

“For most employers, it has proved to be a day-to-day crisis because when they think they know the answer, the rules change,” said Domenique Camacho Moran, a labor and employment lawyer with the firm Farrell Fritz.

Retailers and their advocates had been among the most vocal critics of the federal government’s vaccine rule, saying it would have exacerbated their struggles to hire or hold onto workers at a time when millions of unemployed Americans remain on the sidelines of the job market.

Some labor lawyers say they believe other companies will follow Starbucks in relaxing or undoing their company mandates.

“A lot of companies were pursuing the vaccine or test requirement only because they were being required to do so,” said Brett Coburn, a lawyer at Alston & Bird.

The Occupational Safety and Health Administration, at the request of President Biden, had issued its so-called emergency temporary standard in November. It told businesses with 100 or more workers to require employees to be vaccinated or test weekly.

John Culver, the chief operating officer at Starbucks, said in his memo Tuesday announcing the change in the company’s plans that more than 90 percent of Starbucks workers in the United States had disclosed their vaccination status and that “the vast majority” were fully vaccinated.

“I want to emphasize that we continue to believe strongly in the spirit and intent of the mandate,” Mr. Culver wrote.

The company’s move comes as it faces a growing effort among its work force to unionize. Two weeks ago, employees at a unionized Buffalo-area store walked out, protesting what they said were unsafe working conditions. Some said they were dismayed to see the vaccine rule dropped.

Starbucks Workers United, a union that represents two Buffalo-area stores, expressed frustration that the decision was made without their comment.

“Starbucks reversed their vaccine mandate without discussing the issue, or negotiating about it, with the unionized partners,” the union said in a statement.

For its part, Starbucks maintained that its vaccination requirement had been introduced only because of the federal government’s standard, which the Supreme Court then blocked.

“It was not our own independent policy,” said Reggie Borges, a spokesman for the company. “We knew OSHA was requiring it, the Supreme Court hadn’t ruled on it one way or the other and we needed to make sure our partners were supported and prepared to be in compliance.”

Some major employers, including Walmart and Amazon, had held off on issuing broad vaccine requirements while OSHA’s rule was entangled in legal proceedings. Others, including United Airlines and Tyson Foods, made their own rules. A November poll of 543 companies by the consulting firm Willis Towers Watson found that 57 percent either required or planned to require Covid vaccines, including 32 percent that would do so only if OSHA’s rule took effect.

“It’s pretty divided in corporate America,” said Amanda Sonneborn, a partner at the law firm King & Spalding. “There’s those that have chosen to do mandates on their own, those that were following the government’s mandate and those that challenged it.”

Companies weighing vaccinerequirements have grappled with a number of factors, according to Ms. Sonneborn, including concerns about labor shortages, the political perception of mandates and the need to keep workers safe.

Starbucks said earlier this month that workers would have to disclose their vaccination status by Jan. 10.

“It made me feel a little bit better knowing I was working with people who were vaccinated,” said Kyli Hilaire, 20, a barista who participated in the unionized store’s walkout over safety concerns.

“You see people every day, you work closely with them, there’s not much of an opportunity for distancing,” Ms. Hilaire said. “The number of customers coming into the space makes you cautious. I try to double mask but sometimes it can be difficult to breathe.” Starbucks “strongly recommends” customers wear facial coverings in stores, and requires it where mandated by local laws.

Starbucks also announced a variety of new Covid-19 safety protocols on Tuesday. Workers are now required to wear three-ply medical grade masks, which the company said are available in stores, and isolation guidelines have been expanded to cover anyone who has been exposed to Covid-19, even if they are fully vaccinated.

The company continues to encourage its employees to get the vaccine and booster, and offers two hours of paid time off for getting the shots.