The Supreme Court on Thursday announced it would fast-track its review of a challenge by several death row inmates to the Trump administration’s revised approach to federal executions.

The four inmates, most of whom are scheduled to be killed next month, argue that a lethal injection protocol that the Department of Justice (DOJ) adopted last year violates federal law.

The justices on Thursday ordered the DOJ to respond to the inmates’ petition for appeal by the following day.

A federal execution has not been carried out since 2003, due in part to a widespread shortage during the Obama administration of lethal injection drugs in the so-called three-drug cocktail.

Attorney General William Barr announced last July that federal capital punishment would resume with the use of a single drug, pentobarbital sodium.

At issue is whether the Trump administration’s drug protocol violates the Federal Death Penalty Act, which says that the state where a capital crime was committed should determine the method of execution.

In April, the D.C. Circuit panel ruled 2-1 in favor of a Trump administration plan to resume federal death sentences under a new lethal injection protocol, prompting the inmates’ appeal to the Supreme Court.

On Monday, Barr scheduled the executions to take place in July and August.