In upholding a 2024 ruling by a lower court, the 9th U.S. Circuit Court of Appeals found that the law violates the Second Amendment. Voters passed the law in 2016 and it took effect in 2019.

Many states, including California, make people pass a background check before they can buy a gun. California went a step further by requiring a background check, which costs either $1 or $19 depending on eligibility, every time someone buys bullets.

Last year, U.S. District Judge Roger Benitez decided that the law was unconstitutional because if people can’t buy bullets, they can’t use their guns for self-defense.

The 9th Circuit agreed. Writing for two of the three judges on the appellate panel, Judge Sandra Segal Ikuta said the law “meaningfully constrains” the constitutional right to keep arms by forcing gun owners to get rechecked before each purchase of bullets.

“The right to keep and bear arms incorporates the right to operate them, which requires ammunition,” the judge wrote.

Democratic Gov. Gavin Newsom, who supported the background checks, decried the court’s decision.

“Strong gun laws save lives — and today’s decision is a slap in the face to the progress California has made in recent years to keep its communities safer from gun violence,” Newsom said in a statement. “Californians voted to require background checks on ammunition and their voices should matter.”

The California Department of Justice said the state needs “common-sense, lifesaving” laws that prevent ammunition from falling into the wrong hands.

“We are deeply disappointed in today’s ruling — a critical and lifesaving measure that closes a dangerous loophole,” the department said in a statement. “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.”

Chuck Michel, president and general counsel of the California Rifle & Pistol Association, called the law “absurdly restrictive.”

“This case has been a long hard fight against overreaching government gun control, but a firearm cannot be effective without the ammunition to make it operable. The state of California continues to try to strip our rights, and we continue to prove their actions are unconstitutional,” Michel said.

The law remained in effect while the state appealed the lower court’s decision. Benitez had criticized the state’s automated background check system, which he said rejected about 11% of applicants, or 58,087 requests, in the first half of 2023.

California’s law was meant to help police find people who have guns illegally, such as convicted felons, people with certain mental illnesses and people with some domestic violence convictions. Sometimes they order kits online and assemble guns in their home. The guns don’t have serial numbers and are difficult for law enforcement to track, but the people who own them show up in background checks when they try to buy bullets.

John Parkin, president of Coyote Point Armory in Burlingame, California, said the law made it difficult or impossible for some legal gun owners to purchase ammunition. For example, out-of-state residents and California residents with old guns couldn’t buy bullets because they weren’t in the database of approved gun owners, he said.

“It was written to make California gun owners angry. There wasn’t a lot of logic to it,” Parkin said about the law. “I think there are better ways to keep the public safe.”

California has some of the nation’s toughest gun laws. Many of them are being challenged in court in light of a U.S. Supreme Court decision that set a new standard for interpreting gun laws. The decision said gun laws must be consistent with the nation’s historical tradition of firearm regulation.

Two other California gun laws were struck down in recent years — one that banned detachable magazines that can hold more than 10 bullets and another that banned the sale of assault-style weapons. Those decisions have been appealed. Other laws being challenged include rules requiring gun stores to have digital surveillance systems and restrictions on the sale of new handguns.