DES MOINES, Iowa — A California law approved by voters that promises to get breeding pigs out of narrow cages that prevent them from standing or turning finally took effect Saturday, after years of delays and warnings that the rules could lead to price spikes and pork shortages.

But it will be six months before California grocery shoppers can be sure that pork chops they buy under the new law will be from a pig whose mother wasn’t confined in a so-called gestation crate.

That’s because while the U.S. Supreme Court upheld the law, the state recently agreed to allow pork slaughtered before July 1 to be sold in California markets and restaurants for the rest of the year. That decision gives farmers and grocery stores time to adjust. But it’s exasperating to supporters of the new rules that the effective implementation of the law would again be delayed — four years after voters approved it.

“This development compounds the instability and confusion in the marketplace, while punishing the small independent family farmers and those companies that have been prepared to abide by the law,” Chris Oliviero, general manager of meat company Niman Ranch, said in a statement.

Niman stands to benefit from the law because it contracts with farmers that have long met California’s new animal welfare rules.

But even backers of the tougher rules recognize a silver lining in the delay: Giving producers, grocers and restaurants more time to adjust will reduce the chance of shortages. Josh Balk, who led the Humane Society of the United States’ campaign to pass the law, said “there’s going to be a smooth transition for the pork industry.”

The measure also included space requirements for egg-laying hens and veal calves. But while those producers complied, the pork industry filed legal challenges. They argued that California, which consumes roughly 13% of the nation’s pork but produces almost none of it, shouldn’t dictate how farmers mainly in the Midwest and North Carolina should raise hogs.

Californians approved Proposition 12 in 2018, mandating that fresh pork sold in their state had to be born to sows with at least 24 square feet of space, allowing a breeding pig to turn around and extend its limbs. It effectively banned widely used gestation crates that protect sows from other pigs, which can be aggressive, but that many people see as cruel.

Producers argued converting barns to comply would be costly, with standard operations paying $5 million to $15 million, said Michael Formica, a lawyer with the Iowa-based National Pork Producers Council. Larger spaces would also mean higher heating and maintenance costs.