Days after a foie gras ban came into force in California, a Los Angeles restaurant group and others have filed a lawsuit seeking to overturn the bill outlawing the controversial delicacy.

AFP reports that Hot's Restaurant Group, Canada's Association des Eleveurs de Canards et d'Oies du Quebec and New York-based producer Hudson Valley Foie Gras claim the ban is "unconstitutional, vague and interferes with federal commerce laws."

Foie gras -- fattened liver of a duck or goose, usually by force-feeding corn to the bird --was the target of animal lovers who persuaded the state legislature to ban it.

The legal challenge claims the 2004 law is unclear in defining what constitutes force-feeding, said attorney Michael Tenenbaum, who filed the lawsuit in Los Angeles this week.

California lawmakers agreed the ban in 2004, but allowed for a grace period of seven and a half years to comply before it came into effect on July 1 this year. Restaurants serving the gourmet item can be fined up to $1,000.

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Meanwhile, the OC Register is reporting that some restaurants continue to use foie gras.  The day after the ban Antoine Price, owner of Cafe Mimosa in San Clemente, served up a meal titled "Foie You!," where foie gras was the centerpiece of all seven dishes --including dessert.

"They can lock me up if they want," Price told the Register. "I don't mind."