Sandoval maintained the state screenings are more thorough than federal checks because they include buyer mental health and criminal records relating to domestic violence, misdemeanor crimes, arrest reports and restraining orders.

Laxalt issued a legal opinion saying the initiative impossibly required the governor to have the FBI expend federal resources to enforce a state law. The FBI said it would not do so, he said.

Initiative proponents said the Nevada Background Check Act would tighten requirements and stop “felons, domestic abusers and other people with dangerous histories” from buying guns from unlicensed sellers.

They sued to enforce the initiative just days after 58 people were killed and more than 800 were injured last Oct. 1 in the deadliest mass shooting in modern U.S. history on the Las Vegas Strip.

Proponents conceded the measure would not have prevented the Las Vegas gunman from legally obtaining the assault-style weapons he used.

But they said it could help keep guns out of the hands of people who should not have them by increasing the number of buyers required to undergo background checks.