A Maine federal judge on Monday issued a ruling preventing the Trump administration from implementing changes to a drug discount program used by hospitals while a lawsuit filed against the federal government is pending.

St. Mary’s Regional Medical Center in Lewiston, the Maine Hospital Association, the American Hospital Association and several other hospitals filed a lawsuit in U.S. District Court in Portland this month to stop the federal pilot program.

The pilot program proposed by the U.S. Department of Health and Human Services would change the 340B drug discount program from the current model, where hospitals obtain the drugs at a discount upfront, to a rebate system.

Hospital groups said Maine hospitals could lose millions under the pilot program, which federal health and human services officials say is intended to prevent improper use of the drug discount program.

Chief Judge Lance Walker, who granted the preliminary injunction Monday, said in his ruling that the Trump administration failed to follow the Administrative Procedures Act when starting the pilot program.

“As complicated as certain aspects of this case might seem, it boils down to a simple principle. Defendants cannot fly the plane before they build it,” Walker said in the ruling.