Animal rights activists have asked a state judge to stop foie gras production in New York, saying the ducks used are overfed to such an extent that they are diseased and unfit for sale under state law.

The lawsuit, if it succeeds, could spell the end of foie gras production in America, a goal animal rights groups have long sought. The two Sullivan county farms that are defendants in the suit are the only foie gras producers in the country, other than a Northern Californian foie gras farm that may shut down under a California state law banning the industry.

The suit comes on the heels of Chicago’s recently imposed ban of the delicacy, which comes from the fattened liver of force-fed ducks and geese.

Yesterday’s suit, filed in state Supreme Court in Albany, represents an unusual turn to the courts by opponents of the foie gras industry, who have mostly focused their attentions on encouraging legislators to enact bans, legal observers say.

“It sounds creative,” a professor at Michigan State College of Law who closely follows animal rights litigation, David Favre, said. “This is a new approach.”

The plaintiffs, who include the state and national humane societies, claim that foie gras should be considered an “adulterated” food product because the ducks grow so unnaturally fat and ill that they qualify as diseased under state agriculture law, according to the complaint. It is illegal to sell the products of diseased animals under state law. The suit accuses the commissioner of New York State Department of Agriculture and Markets, Patrick Brennan, for not classifying foie gras as an “adulterated” food and taking it off the market, according to the complaint.

One of the foie gras producers being sued, Hudson Valley Foie Gras, disagrees with calling the 1,000 ducks usually on site diseased.

“Last I checked, we haven’t been shut down by any regulators,” a company official, Allison Lee, said.

Ms. Lee said a federal United States Department of Agriculture regulator is on the killing floor every day it is open to “make sure everything is kosher, not literally kosher, but in compliance with federal law.”

Whether a judge will decide if the ducks should be considered diseased remains to be seen. A judge could decide that the Legislature intended for the law to only “concern itself with animals whose diseased state could then cause diseases in humans,” a professor at the University of California at Los Angeles, Tamie Bryant, who specializes in animals and the law, said.

“You could argue that the consumption of something that high in fat is a health hazard,” Ms. Bryant said.

Calls left with the other New York foie gras producer, Bella Poultry, were not returned.

A spokeswoman for the state’s Department of Agriculture and Markets declined to comment.

The Humane Society has unsuccessfully called for one of the foie gras farms to be prosecuted for animal cruelty, the attorney who heads farm animal litigation for the Humane Society, Carter Dillard, said.

The first challenge the suit faces is to convince a judge that the animal-rights activists who filed the suit have suffered enough harm to allow them standing to sue. The plaintiffs in yesterday’s suit offered several ways that they had been harmed by the foie gras industry.

One plaintiff, Caroline Lee, claims that the state’s regulatory departments are misspending her tax dollars by inspecting birds raised for foie gras production without concluding they are diseased. Another plaintiff, an animal rescue organization, Farm Sanctuary, claims its employees have been “aesthetically and emotionally injured” by being exposed to the “suffering” of abandoned ducks that they rescue from foie gras production. Another plaintiff, a New York restaurateur, Joy Pierson, claims that her decision not to serve foie gras has caused her to lose customers at her two Manhattan restaurants, Candle 79 and Candle Café, according to the complaint.