The Texas Department of Criminal Justice is suing the U.S. Food and Drug Administration over an impounded shipment of drugs to be used for lethal injections.

More than 17 months ago, the FDA detained 1,000 vials of sodium thiopental meant for the Texas Department of Criminal Justice. The drugs remain in federal custody, according to the lawsuit, which was filed Tuesday.

Lethal injection is the primary means of execution in all 31 states that use the death penalty. With supplies of lethal injection drugs running low, states have found alternatives from foreign suppliers. The particular shipment of drugs involved in this case came from an unnamed foreign supplier, court documents show.

Texas argues the FDA is required by law to make a decision on the drugs’ admissibility “within a reasonable time.” The Texas Department of Criminal Justice is requesting the court declare the delay unlawful, forcing the FDA to make a final decision on the drugs.

“The FDA does not comment on possible, pending or ongoing litigation,” Lyndsay Meyer, an FDA press officer, told CNN.

Lethal injection initially required a three-drug cocktail: The first, sodium thiopental or pentobarbital, puts the prisoner to sleep; the second, pancuronium bromide, brings on paralysis and the final agent, potassium chloride, stops the heart.

In 2010, European drug manufacturers began to ban exports of the cocktail ingredients to the United States. The following year, concerned about the use of sodium thiopental in executions, Illinois-based Hospira stopped making the drug, and Denmark-based Lundbeck banned US prisons from using its pentobarbital. The United Kingdom also introduced a ban on exporting sodium thiopental, and the European Union took an official stance in 2012 with its regulation on products used for capital punishment and torture.

States with the death penalty began looking for alternatives. Among them: procuring the drugs from alternative sources, devising a one-drug method, employing other drugs such as midazolam or propofol, and using controversial compounding pharmacies to manufacture the drugs.