Utah Gov. Gary Herbert signed a bill Monday making the firing squad the method of execution if the state can't come up with the drugs for lethal injections.
State lawmakers approved the bill earlier this month, making Utah the latest state to look for alternative methods in the wake of nationwide drug shortages. Death penalty opponents have been urging the Republican governor to veto it.
"We regret anyone ever commits the heinous crime of aggravated murder to merit the death penalty, and we prefer to use our primary method of lethal injection when such a sentence is issued," said Marty Carpenter, a spokesman for Herbert.
"However, when a jury makes the decision and a judge signs a death warrant, enforcing that lawful decision is the obligation of the executive branch," Carpenter said.
The last person executed by firing squad was Ronnie Lee Gardner in 2010. Because he was convicted before 2002, he had the option of choosing the bullet over the needle. The new law will let the state impose the firing squad.
Gardner's brother, Randy Gardner, called the move "pretty backwoods" and scoffed at claims by the law's proponents that the firing squad is more humane than other methods.
"There's no humane way to execute anyone," the brother said. "I had the opportunity to see my brother after four bullets hit his chest, and I could have put my hand in anyone of the holes. It didn't look very humane to me.
"He was tied down with a hood over his head. Terrorists around the world and ISIS — when they execute people, that's what they do."
Utah has eight inmates on death row. Other states that have run low on execution drugs have considered the electric chair and the gas chamber as backups.