Backers of a blocked ballot measure requiring background checks on private gun sales and transfers are threatening to sue Republican Gov. Brian Sandoval and the state if they do not immediately implement it.

In a letter dated Sept. 25, attorney Mark Ferrario — representing Nevadans for Background Checks, the group that backed the ballot question — gave Sandoval and state officials a deadline of Oct. 9 to begin implementing the ballot measure before they turn to the court system to settle the matter.

Though the letter was sent to the governor last week, the issue is all the more ripe in the wake of a mass shooting on the Las Vegas Strip that left 59 dead and 529 injured on Sunday, though it is unclear how the shooter in that incident obtained all his firearms and whether the implementation of the ballot measure would have made a difference. The owner of Guns & Guitars in Mesquite said on Monday that his shop sold firearms to the suspect, 64-year-old Stephen Paddock, but that all necessary background checks and procedures were followed as required by local, state and federal law and that he never gave any indication or reason to believe he was unfit to purchase a gun.

Paddock also purchased a rifle and a shotgun from New Frontier Armony in North Las Vegas in the spring, NBC News reported. He also purchased a shotgun from the Dixie GunWorx store in St. George, Utah, according to the Salt Lake Tribune.

“This is an issue that can and should be easily resolved,” Ferrario wrote. “Given the apparent ease with which the law could be implemented it is difficult to understand any reluctance to carry out the people’s mandate.”

Ferrario said he met with Sandoval’s former top attorney in May and submitted a detailed legal memorandum explaining the group’s view that Attorney General Adam Laxalt and state officials presented the governor with an “incomplete and potentially misleading set of options” when it came to implementing the new law, and had even effectively prohibited private gun sellers from even the option of using the federal background check system.

“Yet, regrettably, so far as I am aware, since the submission of our Memorandum, no steps have been taken to see that the Background Check Initiative Act is implemented and that the will of the people of Nevada is honored,” Ferrario wrote. “In the meantime, as the Memorandum also lays-out, the public safety of Nevadans continues to be put at risk every day as private firearms sellers currently have no ability to obtain a background check for prospective buyers under any circumstances.”

In a statement, Sandoval spokeswoman Mari St. Martin said that the state was operating off the advice of the attorney general's office and the FBI, and that state-run background checks were more thorough than those using the FBI's system because Nevada's system can more easily find outstanding warrants, arrests, citations and domestic violence protection orders than its federal counterpart.

"Because of these enhanced background checks, the Governor is committed to maintaining Nevada’s status as a point of contact state; however, the Governor will request an opinion from the Attorney General’s Office on whether the state may legally operate as a dual POC state," she said in an email.

Representatives for the attorney general’s office did not immediately respond to a question for comment about the letter Tuesday morning.

In a later statement, Everytown for Gun Safety president John Feinblatt said it was "unconscionable" for Sandoval to go back to Laxalt for an opinion on what the state should do.

"He doesn’t need another opinion from the attorney general—particularly not the same attorney general who starred in the NRA’s ads opposing this law," he said in a statement.

Voters approved Question 1 on a razor-thin margin — a mere 9,899 votes out of more than 1.1 million cast during the 2016 election — with many high-profile Republicans including Sandoval and Laxalt publicly opposed.

But implementation of the ballot measure, which requires private persons wishing to privately sell or transfer a firearm to first run a background check with a licensed firearm dealer excluding some limited exception like to family members or temporary transfers, hit a snag in December when Laxalt’s office issued an opinion calling the measure “unenforceable.” It was supposed to go into effect on Jan. 1.

Citing an advisory from the Federal Bureau of Investigation, Laxalt’s office said it could not enforce the ballot measure given the federal agency’s refusal to follow through on the ballot measure’s requirement that background checks for private sales or transfers use the federal government’s system rather than the state’s.

“When a law imposes a requirement that cannot be performed, a party is relieved of compliance until the obstacle to performance is lifted,” his office wrote.

Though Nevada is a so-called “point of contact” (POC) state for firearm purchases — meaning the Nevada Department of Public Safety serves as the state point of contact for background checks on firearm sales instead of the FBI — Ferrario argues that Nevada voters chose to not be a POC state for private gun sales by passing Question 1.

Federal law typically requires background checks on firearm sales from licensed gun dealers, but 12 states, including Nevada, took on that responsibility in the late 1990’s by developing their own systems.

But in a lengthy legal memorandum submitted to the governor’s office and obtained by The Nevada Independent, attorneys for the ballot question argued that the measure’s passage essentially required the state to move from a “full” to “hybrid” POC system, which likely requires an official action from the governor’s office to revise Nevada’s 1998 decision to run its own background check system.

“Notably, the Attorney General’s opinion accepted the FBI’s position without attempting any analysis of whether that position was justified, including a total failure to consider whether the Background Check Law had changed Nevada from a full to a partial POC state,” Ferrario wrote.

The memorandum also accuses the state’s Department of Public Safety of presenting the governor with a “false binary choice” after the ballot measure was approved that did not take the partial POC option into consideration. It lays out several examples of “hybrid” states where the federal system is used for certain types of firearm sales and the state’s individual system is used for others.

Mark Ferrario, Nevadans for Background Checks Letter to Sandoval on Question 1 by Megan Messerly on Scribd