The justices decided unanimously to overturn two lower court rulings tossing out the legal challenge. The lower courts had sided with grocers, who said such labeling disputes should be resolved by the U.S. Food and Drug Administration and not through lawsuits.

But the Supreme Court ordered the deceptive marketing lawsuit reinstated, ruling that private citizens can file such challenges because of an identical state law requiring labeling.

"Congress appears to have made a conscious choice not to preclude such actions," Justice Carlos Moreno wrote.

The lawsuit was filed by 11 consumers and backed by California Attorney General Jerry Brown. The suit names some of the state's largest grocers, including Albertson's Inc., Safeway Inc., The Kroger Co., Trader Joe's, Costco Wholesale Corp., Whole Foods Market Inc., Bristol Farms Inc. and Ocean Beauty Seafoods Inc.

The consumers allege that farmed salmon are naturally grayer than wild-caught fish. But fish farmers feed the salmon two chemicals that make their flesh redder and nearly identical looking to wild salmon.