A U.S. federal appeals court issued a stay Saturday freezing the Biden administration’s efforts to require workers at U.S. companies with at least 100 employees be vaccinated against Covid-19 or be tested weekly, citing “grave statutory and constitutional” issues with the rule.

The ruling from the United States Court of Appeals for the Fifth Circuit comes after numerous Republican-led states filed legal challenges against the new rule, which is set to take effect on Jan 4.

The White House declined to comment on the ruling, and referred questions to the Labor Department.