A supplier of Texas' execution drugs can remain secret under a court ruling that cited a risk of "physical harm" to the compounding pharmacy if the information became public.

The Texas Supreme Court's decision Friday ends a long-running legal battle that began in 2014 over the drugs used in the nation's busiest execution chamber.

Defense attorneys argued that the supplier identity was needed to verify drug quality and spare condemned inmates from unconstitutional pain and suffering. Texas officials have said disclosing the source would "threaten the death penalty's operation nationwide."

Availability of execution drugs has become an issue in many death penalty states. The Texas decision only applies to drugs used in a few past executions, since Republican Gov. Greg Abbott signed a law in 2015 making supplier records secret.