AUSTIN, Texas (Reuters) - Texas must reveal the source of the drugs it uses for executions, its Supreme Court affirmed on Friday, rejecting the state’s arguments that doing so could lead to physical harm of the supplier and impede lethal injections.

FILE PHOTO: The death chamber and the steel bars of the viewing room are seen at the state penitentiary in Huntsville, Texas, U.S. on September 29, 2010. Courtesy Jenevieve Robbins/Texas Department of Criminal Justice/Handout via REUTERS/File photo

Ever since a sales ban of lethal injection drugs by major pharmaceutical companies a few years ago, most states have kept the suppliers of their drugs secret. This has prompted lawsuits on behalf of death row inmates, arguing that prisoners could be subjected to unconstitutional suffering from faulty drugs in lethal injection mixes from questionable suppliers.

The Texas Supreme Court on Friday affirmed a May 2017 decision by an appellate court that said there was not enough compelling evidence provided by the state to show that there was a substantial threat of physical harm.

“Today’s decision is a win for the fundamental principles of transparency and open government,” Maurie Levin, one of the attorneys who helped bring the lawsuit on behalf of two Texas death row inmates, said in a statement.

The Texas Department of Criminal Justice said in a statement that it intends to file a motion with the court for a rehearing.

Texas has executed 551 people since capital punishment was reinstated in 1976, 37 percent of all U.S. executions and more than triple any other state, according to the Death Penalty Information Center.

Texas has also been one of the few states in the country able to procure a steady supply of execution drugs.

In 2016, pharmaceutical company Pfizer Inc PFE.N joined a sales ban imposed years earlier by major European drug makers that did not want their products used in executions due to ethical concerns. This caused many states to scramble for suppliers and a few to suspend executions due to lack of drugs.

Although 31 states have the death penalty, only eight have held executions since Pfizer’s decision, which cut off the last major U.S. source for drugs in the lethal mixtures.

Many have turned to lightly regulated compounding pharmacies, which can mix chemicals. The states also have banned the release of the pharmacies’ names, which they have said was a security precaution.

For its lethal injection, Texas uses the barbiturate pentobarbital.