Not far from Philadelphia, New York, and Washington, Sauder's Quality Eggs in Lancaster County is ideally situated to serve the more than 50 million consumers in the U.S. Northeast.

But some of the trucks that might have rolled out of Sauder's facilities toward Manhattan are now heading thousands of miles west.

"We're getting lots of calls from California," owner Paul Sauder, 64, said, wearing a white protective suit and speaking over the din of 17,000 clucking brown hens. "Stores are worried they won't be able to meet demand after Jan. 1."

That's when a California law takes effect that requires eggs sold in the nation's most-populous state to come from farms meeting minimum living standards sought by animal-welfare groups, chiefly more cage space.

Passed by voters in a 2008 initiative and expanded two years later, the rules have drawn a lawsuit from a half-dozen states and concern that the idea will spread to other agricultural products. Consumers, too, may be affected: California is the biggest U.S. egg-consuming state, importing more than 30 percent of its eggs, and its requirements affect farms across the country.

Rising meat prices have made eggs a popular alternative and driven per-capita consumption to its highest level in decades. California's law could push up grocery prices as farmers boost their use of costlier cage-free housing or reduce the number of birds in cages.

Sauder's cage-free chickens are laying eggs that command a premium and that are finding ready buyers in California.

"It wouldn't normally make any economic sense to transport eggs to California when I can sell in New York," said Sauder, president of R.W. Sauder Inc. "But if the premium's high enough, I can find a truck or two."

He also has birds living in cages that meet the industry standard: an average of 67 square inches for each, or a patch of ground slightly larger than 8-inches square.

California says that when nine or more chickens are housed in a cage, there must be an average of at least 116 square inches - roughly equal to a 10.7-inch square - of floor space for each bird.

That has farmers rushing to modify their coops while California agriculture agents crisscross the country to certify operations.

Disagreement over how to apply the law is making matters difficult for producers. The California Department of Food and Agriculture interprets the rules as requiring the 116-square-inch standard. The Humane Society says the initiative voters passed really means cage-free, raising the possibility of a lawsuit.

Trade groups that fought the new rules haven't given up. A federal suit filed by six states - including Iowa, the No. 1 U.S. egg producer - said the law was an unconstitutional restraint on interstate commerce. The case was thrown out in October; the states are appealing.

"If they do it for eggs, why can't they do it for pork?" asked Dave Warner, a spokesman for the National Pork Producers Council in Washington. "I'm not sure I want some bureaucrat telling a farmer the best way to care for animals."

The movement for bigger cages is part of a larger consumer trend toward food that's perceived as more humane and sustainable, said Chad Gregory, CEO of the United Egg Producers. The industry can and will adapt, he said.

In Lancaster County, it already has.

John Ebersol, 30, an Amish farmer who sells eggs to Sauder, began raising cage-free hens three months ago. Without the cost of building cages, start-up expenses are lower, though gathering eggs laid on the ground takes time.

As chickens scurried around his ankles, he said: "We have to train them not to do that."