The US Food and Drug Administration is going to court to secure supplies of sodium thiopental, a drug used in lethal injections.
The substance is a short-acting, barbiturate general anaesthetic used in conjunction with other chemicals to execute prisoners.
Supplies of the drug have fallen since 2010 when Hospira, the only US manufacturer of sodium thiopental, ended production because of death-penalty opposition from overseas customers.
Stocks dwindled further in March 2012 after its importation to the US was banned.
A US district judge ruled in favour of 21 prisoners on death row who argued that the FDA didn't have the right to allow prisons to import the drug without ensuring that it would work effectively.
However, under pressure from many of the 33 states that use the lethal injection method, the FDA is now appealing that ruling, reports the BBC.
Image: A gurney in the San Quentin State Prison in the US on which prisoners are restrained during an execution by lethal injection. Photo courtesy of: CACorrections.