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 become one of the first major retailers to backtrack on 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. 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 on to workers when millions of unemployed Americans remain on the sidelines of the job market.