The US Supreme Court has blocked President Joe Biden's rule requiring workers at large companies to be vaccinated or masked and tested weekly.
The justices at the nation's highest court said the mandate exceeded the Biden administration's authority.
The administration said the mandates would help fight the pandemic.
Former President Donald Trump cheered the court's decision, and said vaccine mandates "would have further destroyed the economy".
"We are proud of the Supreme Court for not backing down," he said in a statement.
The administration's workplace vaccine mandate would have required workers to receive a Covid-19 shot, or be masked and tested weekly at their own expense.
According to a majority of the Supreme Court, Mr Biden had the law on his side when ordering healthcare workers to get vaccinated, but using a 51-year-old workplace safety statute to implement a vaccine-or-test requirement on all large employers was a bridge too far.
In a 6-3 decision, the justices agreed with that argument, saying that the workplace safety rule for large employers was too broad to fall under the authority of the Department of Labor's Occupational Health and Safety Administration to regulate workplace safety.
The court's three liberal justices opposed blocking the vaccine mandate, saying such a decision "stymies the federal government's ability to counter the unparalleled threat that Covid-19 poses to our nation's workers.".
The Biden administration had estimated that instituting a vaccine requirement at big employers would save 6,500 lives and prevent 250,000 hospital admissions over six months.
But the National Federation of Independent Businesses, a lobby group that was one of the lead plaintiffs challenging the government's workplace vaccine rule, had charged that it would burden small-business owners with new compliance costs, make it harder to fill positions and lead to lost profits and lost sales?
Supreme Court blocks Joe Biden's vaccine mandate