The justices on Tuesday rejected a challenge to the law from producers of the delicacy in New York and Canada.
Foie gras is the fatty liver of a force-fed duck. The California law bars state farmers from force-feeding birds with a tube, the way foie gras is made. The law also bans the sale of foie gras in California.
Lower courts in California earlier dismissed efforts to block the law from being enforced.
The case is Association des Eleveurs du Quebec, 13-1313.