LITTLE ROCK — A lawsuit filed Friday on behalf of six condemned killers contends Arkansas’ new lethal injection law is unconstitutional and seeks to block executions.

The lawsuit filed in Pulaski County Circuit Court contends that the new law, adopted this year in response to a state Supreme Court decision that declared a 2009 law unconstitutional, violates death-row inmates’ right to die quickly by allowing prison officials to use a slow-acting barbiturate in a mix of chemicals for lethal injections.

The law in effect when the crimes were committed required the state to use fast-acting chemicals, and the new law violates "the well-settled state law principle that a sentence must be in accordance with the statutes in effect on the date of the crime," according to the lawsuit.

The new execution procedure authorized in Act 139, the 2013 Method of Execution Act, permits use of an anti-anxiety drug and phenobarbital, a slow-acting barbiturate. The lawsuit termed the concoction "a completely untried combination and quantity of drugs that will take hours to be injected and to reach their peak effect, that will produce agonizing and degrading effects during the procedure, and that will severely and permanently injure — but may not kill — the prisoners."

"We’re asking for a declaration that the new statute and the procedures that have been promulgated under it are unconstitutional and illegal, and we’re asking a judge to prohibit any executions," said Little Rock lawyer Jeff Rosenzweig.

Aaron Sadler, spokesman for state Attorney General Dustin McDaniel, said McDaniel’s office had received a copy of the lawsuit and was reviewing it.

Rozenzweig filed the lawsuit on behalf of death-row inmates Stacey Johnson, Jack Jones, Jason McGehee, Bruce Ward, Kenneth Williams and Marcel Williams.

The six had been under stays of execution that the Supreme Court granted in 2010 while the inmates challenged the constitutionality of the lethal injection procedure in the 2009 law. Earlier this month, the high court declared those stays were no longer in effect and said the inmates would have to take their case to circuit court if they wanted to challenge the new lethal-injection law.

Last year, the court ruled that the 2009 law gave too much discretion to the director of the state Department of Correction, in violation of the constitutional doctrine of separation of powers. In response, the state Legislature passed Act 139.

The attorney general’s office petitioned the court to lift the stays of execution in March, shortly after Act 139 became law, arguing that the new law removed the issues that the inmates had challenged.