A federal judge on Thursday blocked a California law set to take effect Saturday that would have barred gun owners from possessing high-capacity ammunition magazines.
The judge ruled that the ban approved by the Legislature last year takes away gun owners' Second Amendment rights and amounts to the government taking people's private property without compensation.
California law has prohibited buying or selling the magazines since 2000, but until now allowed those who had them to keep them.
"If this injunction does not issue, hundreds of thousands, if not millions, of otherwise law-abiding citizens will have an untenable choice: become an outlaw or dispossess one's self of lawfully acquired property," San Diego-based U.S. District Judge Roger Benitez wrote.
He issued a preliminary injunction blocking the law from taking effect while he considers the underlying lawsuit filed by the National Rifle Association-affiliated California Rifle & Pistol Association.
A Sacramento-based judge is considering another challenge filed by different firearm owners' organizations.
State lawmakers approved the ban last year as part of a package of bills adding to what already were some of the nation's strictest gun laws. Voters agreed in November when they approved Proposition 63, a measure that toughened the penalties by allowing violators to be fined or jailed.
California Attorney General Xavier Becerra, who is defending the state law, did not immediately comment.
Supporters say that magazines often holding 30 or 100 bullets are typically used in mass shootings and aren't needed by hunters or civilian owners.
Forcing assailants to change magazines more frequently gives victims time to flee or subdue the shooter, Becerra argued in court filings.