(Reuters) - A U.S. appeals court ruled on Friday that an Arkansas law restricting the use of the so-called abortion pill could proceed, overturning a lower court’s decision in 2015 that blocked the law a day before it was to go into effect.

The 8th U.S. Circuit Court of Appeals in St. Louis sent the case back to the federal district court in Little Rock, telling the court it must estimate approximately how many women would likely be harmed by the law before the case could proceed further.

Planned Parenthood Great Plains, which runs two of the three clinics providing abortions in Arkansas, sued the state in 2015, saying the law would deprive many Arkansas women of their right to an abortion.

The law requires that any doctor dispensing abortion-inducing drugs sign a contract with another doctor who would agree to handle any medical complications that might stem from the drugs. The contracted doctor must have admitting privileges at a hospital designated to handle emergencies related to abortion pills.

Planned Parenthood said it ran a 24-hour telephone helpline for patients and that medical complications were extremely rare, but that in those instances its doctors and nurses already have procedures to ensure a patient receives any care they need at a nearby hospital.

U.S. District Judge Kristine Baker sided with Planned Parenthood in 2015, concluding that it would not be able to find such a doctor and be forced to stop offering abortion services at its clinics in Little Rock and Fayetteville.

Women in Fayetteville, for example, would then have to make two 380-mile (610-km) round trips to get an abortion at what would be the state’s last remaining abortion clinic, Baker’s ruling said.

Ruling that this was an undue burden on those women and that Planned Parenthood would likely win its lawsuit, Baker granted a preliminary injunction stopping the law from taking effect.

On Friday, the appeals court overturned that injunction. The ruling said the district court had “abused its discretion” and criticized it for not determining even approximately how many women would be affected.

Planned Parenthood could win its case if the court found a “large fraction” of women seeking abortion-inducing drugs would face an undue burden, but the lower court failed to determine this, the ruling said.

Arkansas Attorney General Leslie Rutledge welcomed the ruling, saying in a statement that “Planned Parenthood failed to show that the state law is a substantial obstacle preventing most women from having access to abortion services.”

Danielle Wells, a spokeswoman for Planned Parenthood Federation of America, said the organization was mulling its next steps, but noted it would have two weeks under the appeals court rules to petition for a rehearing.

“This law was written by politicians, and not doctors, and is part of a national strategy to end access to abortion step by step and law by law,” Wells wrote in an email.