State officials and gun control advocates are raising alarms about the future of firearm safety after the 9th U.S. Circuit Court of Appeals on Thursday struck down a California law that requires a background check for people purchasing ammunition.

Under the law, firearm owners had to prove they were registered with the state Department of Justice and were legally allowed to possess guns and ammunition. A federal appeals court declared the requirement unconstitutional in a 2-1 vote, a decision advocates say could jeopardize California’s progress on gun safety.

“We’re really devastated, really hurt and really outraged to sort of see the decision of the court today,” said Christian Heyne, chief officer of policy and programs at Brady United Against Gun Violence. “When you look at the fact that guns are the leading killer of children and young people in this country, we have got to do everything we possibly can in the name of public safety.”