A federal appeals court has ruled that California’s first-of-its-kind law requiring firearm owners to undergo background checks to buy ammunition is unconstitutional.

In a 2-1 vote on Thursday, the ninth US circuit court of appeals in Pasadena upheld a lower court judge’s permanent injunction against enforcing the law.

Circuit judge Sandra Ikuta said the law “meaningfully constrains” people’s right to keep and bear arms, and that California failed to show that the law was consistent with the US historical tradition of firearm regulation, as required under the supreme court’s 2022 Bruen decision.

Thursday’s ruling was a defeat for the gun control movement, albeit one that did not come as a surprise. Gun control and violence prevention advocates had decried the supreme court’s 2022 decision, and argued that the historical twin test would lead to the rolling back of hard-won regulations that they say have been vital in reducing death and injury from gun violence.

Since the ruling, there have been more than 2,000 gun law challenges, and lower courts continue to sort through the new parameters the ruling has produced. Most of the cases were brought by people who were looking to have their gun case convictions overturned, according to the Trace. The others have been civil lawsuits brought by gun rights groups.

The office of Rob Bonta, California’s attorney general, which defended the law, said it was disappointed by the decision.

“Our families, schools, and neighborhoods deserve nothing less than the most basic protection against preventable gun violence, and we are looking into our legal options,” a spokesperson said.

Voters had in 2016 approved a California ballot measure requiring gun owners to undergo initial background checks to buy ammunition, and pay $50 for a four-year ammunition permit.

Legislators amended the measure to require background checks for each ammunition purchase. The background check scheme took effect in 2019.

The case against the law was brought by Kim Rhode, who has won three Olympic gold medals in shooting events, and the California Rifle & Pistol Association (CRPA). Many gun rights groups and 24 mostly Republican-led US states submitted briefs supporting the law’s opponents.

The CRPA described the ruling as a “huge win” for California gun owners.

It said: “Today’s ruling is what plaintiffs … and many in the 2A community, like the National Rifle Association, who supported the many appeals in this case, have been waiting almost a decade to receive.”

In a joint statement, the association’s president and general counsel Chuck Michel called the decision a victory against “overreaching government gun control”, while Rhode called it “a big win for all gun owners in California”.

California was backed by several safety groups. “Background checks for ammunition sales are common sense,” said Janet Carter, managing director of second amendment litigation at Everytown Law.

Last year, nearly 200 people who were on California’s list of people who owned guns but later became prohibited from possessing them were denied from buying ammunition through this background check system, according to the California justice department’s 2024 Armed and Prohibited Persons System Report.

In his dissenting opinion, Judge Jay Bybee, a George W Bush appointee, argued that in most cases, the state’s ammunition background check process “costs one dollar and imposes less than one minute of delay”.

The law “is not the kind of heavy-handed regulation that meaningfully constrains the right to keep and bear arms”, Bybee wrote.

He further argued the majority opinion is flawed and contorts the precedent set by the Bruen decision “beyond recognition”. Thursday’s ruling, he argued, effectively declares unlawful any limits on ammunition sales, given the unlikelihood a state can point to identical historical analogues.