COLUMBIA, S.C. (AP) — The state of South Carolina says an inmate scheduled to be executed next week could be put to death with a lethal dose of just one drug if officials cannot get hold of all three drugs the procedure calls for.

The South Carolina Supreme Court has set a Dec. 4 execution date for Richard Bernard Moore, 55, who has spent nearly two decades on death row following his conviction for the 1999 killing of a convenience store clerk in Spartanburg.

In a letter to Moore's attorneys, the South Carolina Department of Corrections said it reserves the right to execute Moore with a single lethal dose of the sedative pentobarbital, the Herald-Journal first reported Friday.

The state’s usual injection protocol calls for three drugs: pentobarbital, pancuronium bromide and potassium chloride. But the corrections agency has said it has not had the drugs in stock since 2013, when its last supplies expired.

Execution plans could be delayed if the the agency cannot obtain pentobarbital. Securing lethal injection drugs has become an increasingly difficult task in the U.S. as drug manufacturers have shied away from selling to states under pressure from anti-death penalty activists. Corrections chief Bryan Stirling, along with the governor and attorney general, have advocated for a bill to shield the identities of manufacturers who provide such drugs.

A handful of states, including Texas and Georgia, along with the federal system, have most recently used pentobarbital sodium alone in their execution protocols, according to the Death Penalty Information Center.

Moore's team will continue to mount legal challenges in federal court after the South Carolina Supreme Court denied a recent motion to stay the execution, attorney Lindsey Vann told The Associated Press Monday.

Moore's attorneys had argued the court should delay the date because of the dangers the coronavirus pandemic presents to those involved in the execution and those who would witness it.

Attorneys also said the corrections department was withholding information about its execution methods, preventing Moore from making an informed decision between the two death penalty methods provided by state law: lethal injection or electrocution.

Per law, Moore had until Nov. 20 to choose between the two methods. But Moore made no decision as of Friday, Vann confirmed. Without that choice, the method defaults to lethal injection.

Moore's team objected to reviewing information provided by the corrections department last week because it required them to sign a confidentiality agreement that would not have allowed them to confer with medical experts, Vann said.

In court filings, lawyers for the corrections agency and the attorney general's office have characterized the recent litigation as a “last-minute attempt to delay a constitutionally approved punishment.” Vann said Moore has requested information on the execution methods for months.

Moore is one of 37 people, all men, currently on South Carolina's death row. Some prosecutors have sought the death penalty less often in recent years, citing the state's inability to carry out executions.

Prosecutors said Moore attempted to rob a convenience store in 1999 and entered into a gunfight with clerk James Mahoney, who shot Moore in the left arm. Moore fired at Mahoney and a customer, killing Mahoney, they said.