WASHINGTON — The Biden administration on Friday asked the Supreme Court to block part of a court decision that prevents pregnant women from obtaining key abortion drug mifepristone by mail.

Solicitor General Elizabeth Prelogar, representing the Food and Drug Administration, urged the court, which has a 6-3 conservative majority, to put on hold the entirety of a decision issued by Texas-based U.S. District Judge Matthew Kacsmaryk that handed a sweeping victory to abortion opponents.

“This application concerns unprecedented lower court orders countermanding FDA’s scientific judgment and unleashing regulatory chaos by suspending the existing FDA-approved conditions of use for mifepristone,” Prelogar wrote in court papers.

Danco Laboratories, which makes Mifeprex, the brand version of the pill, filed a similar request on Friday.

Danco said it would be “irreparably harmed” if the decision goes into effect because it “will be unable to both conduct its business nationwide and comply with its legal obligations.”

Both the Justice Department and Danco said the court should immediately block Kacsmaryk’s ruling in full while it considers what steps to take. They said the court should weigh whether to quickly hear oral arguments and issue a full ruling on an expedited basis.

Late Wednesday night, the 5th U.S. Circuit Court of Appeals gave the Food and Drug Administration a partial victory by declining to suspend the original FDA approval of mifepristone in 2000, which would have made distribution of the drug unlawful.

But the court allowed separate elements of Kacsmaryk’s decision to remain in place, including a prohibition on obtaining the drug by mail, which is what the Justice Department is contesting at the Supreme Court.

The administration would need to win the votes of at least five of the nine justices on the court, which last summer in a 5-4 ruling overturned the landmark Roe v. Wade ruling that said women have a right to obtain an abortion.

The new case raises different legal issues concerning the the FDA’s process for approving drugs, but will nevertheless put to the test the court’s pledge last year that it would leave abortion policy to the states and federal government.

The appeals court’s decision, if left in place, imperils widespread availability of the drug, as it would require patients to make in-person visits to obtain it. The three-judge panel said part of Kacsmaryk’s decision that suspends changes the FDA made to the drug’s approved use in 2016, could go into effect; it also determined that the agency’s finding in 2021 that mifepristone can be distributed by mail should be put on hold as well as the 2019 decision that approved a generic version of mifepristone, which is made by GenBioPro.

The 2016 changes, among other things, reduced the number of in-person visits that patients are required to make from three to one and allowed the pills to be prescribed to women at up to 10 weeks’ gestation instead of up to seven weeks.

The appeals court concluded that the challengers had waited too long to contest the 2000 approval in court. But the court found the claims against the 2016 revisions and later decisions could be pursued because the government and Danco “have not shown that plaintiffs are unlikely to succeed on the merits of their timely challenges.”

The court also found that a hitherto obscure 19th century law called the Comstock Act, which prohibits the mailing of any drug or medicine that can be used for abortion, factors into its analysis of the 2021 decision to allow mifepristone to be distributed by mail.

Complicating the situation further, a federal judge in Washington state issued a preliminary injunction in a different case Friday barring the FDA from “altering the status quo and rights as it relates to the availability of mifepristone.” 

That ruling applies only to the 17 liberal-leaning states and the District of Columbia that filed a lawsuit in February challenging the FDA’s regulations over the drug. The Justice Department has filed a motion in federal district court in Washington state, asking for clarification of Friday’s ruling.

While a different drug, misoprostol, can be used alone for abortions, experts have said it is not as effective in terminating pregnancies as it is when administered in tandem with mifepristone.

A majority of abortions in the U.S. are carried out with the use of pills, according to a survey conducted by the Guttmacher Institute, a research group that supports abortion rights.