The US government has sought to justify its new coronavirus mandate for large companies in response to a court order blocking the measure.
The administration of President Joe Biden implemented the mandate to help ensure the safety of workers.
Under the rule, companies with 100 or more employees must require workers to get fully vaccinated or alternatively require them to undergo weekly testing and wear masks. The rule must be implemented by January 4 at the latest.
Governors of more than half the states have filed lawsuits, arguing that the rule is unconstitutional.
A federal appeals panel on Saturday issued a court injunction suspending the mandate.
Speaking to reporters on Monday, White House Principal Deputy Press Secretary Karine Jean-Pierre said, "The administration clearly has the authority to protect workers, and actions announced by the president are designed to save lives and stop the spread of COVID-19."
She added that the Justice Department will defend these lawsuits.
Jean-Pierre also noted that the labor secretary "determines workers at risk or what is called 'grave danger.'"
She added that more than 750,000 people have died of the virus, and approximately 1,300 people continue to die a day. She said, "If that's not a 'grave danger,' I don't know what else is."