Briefing is now complete in a lawsuit filed by more than a dozen states asking the United States Supreme Court to block a California law requiring any eggs sold within the state to come from chickens that have sufficient space to stretch out in their cages.

In the lawsuit, filed directly with the high court in December, Missouri, Iowa and 11 other states allege that “California has single-handedly increased the costs of egg production nationwide by hundreds of millions of dollars each year” due to its stringent regulations prohibiting confinement of egg-laying hens. The complaint contends that California’s requirements violate the Constitution’s interstate commerce clause. The lawsuit also alleges that California’s regulations are preempted by the Egg Products Inspection Act (EPIA), a federal law requiring uniformity of labeling, standards, and other provisions allowing for free movement of eggs and egg products in interstate commerce. To support their claims, plaintiffs rely on a study from an economist concluding that the price of a dozen eggs has increased nationwide between 1.8 percent and 5.1 percent since January 2015 due to California’s requirements.

The controversy arises out of California’s Proposition 2, a 2008 ballot measure that requires the state’s farmers give each egg-laying hen at least 116 square inches of space. Proposition 2 specifically forbids a person in California “from tether[ing] or confin[ing]” certain animals, including egg-laying hens, on a farm, “for all or the majority of any day, in a manner that prevents such animal from: (a) Lying down, standing up, and fully extending his or her limbs; and (b) Turning around freely.” The measure passed with nearly two-thirds of the vote. Though referenced colloquially as the “cage-free egg law,” the measure does not specifically prohibit the confinement of egg-laying hens in cages. Farmers may satisfy its requirements simply by reducing the number of chickens in each cage.

In 2010, California legislators expanded the law to require that all eggs sold in California comply with Proposition 2, not just those produced in the state.

These provisions, which became effective in 2015, were met with immediate challenge both within and outside California.

First, several California egg farmers brought suit alleging that Proposition 2 is unconstitutionally vague. These challenges ultimately did not succeed.

Then, in 2014, the state of Missouri and five others challenged the law in federal district court. The district court dismissed the case on standing grounds, ruling that the states failed to show that the law would harm their citizens, instead of a mere potential for future damages to some egg producers. The Ninth Circuit Court of Appeals affirmed the dismissal in 2016, leading the other states to pursue an unsuccessful petition for certiorari in 2017.

In addition to facing constitutional scrutiny, California’s egg regulations have sparked litigation against retailers. Last month, the Animal Legal Defense Fund sued Trader Joe’s in California state court, claiming the grocery chain has been deceptive in the labeling of its eggs. The complaint, which was filed on behalf of a consumer, contends that Trader Joe’s falsely advertises its eggs with images suggesting that the “hens who lay its private label, cage-free eggs are free to roam outdoors, under the sun and in green pastures.” Instead, according to the lawsuit, the cage-free eggs actually come from industrial hen houses, where chickens do not have access to the outdoors. The case is pending in Alameda County and Trader Joe’s has not yet filed a response.

Earlier this year, a class-action lawsuit filed in California federal court alleged that a large retailer deceived shoppers by describing eggs as coming from chickens “free to roam, nest and perch in a protected barn with outdoor access” when the hens were actually kept indoors.

Animal rights advocates in California are seeking to add another ballot measure in November 2018 that would proscribe even more explicit requirements for cage-free eggs. The new initiative would set the standard at 144 square inches per bird — one square foot — which is the level at which a hen is considered by animal activists to be “cage-free.” By 2022, the chickens and other farm animals would be fully cage-free, and be allowed to roam freely inside barns.