Hagens Berman, a consumer-protection law firm, has filed a lawsuit in federal court alleging that ConAgra Foods Inc. (NYSE: CAG) deceptively marketed Parkay Spray, a sprayable margarine product, as “fat free,” and “0 calories” to entice health-conscious customers, despite the product not meeting federal requirements to qualify for those claims.

The lawsuit, filed on March 21, 2013 in the U.S. District Court for the District of Northern California, seeks to represent a nationwide class of consumers who purchased Parkay Spray and who were misled about its nutritional value. The suit asks the court to award damages to consumers to compensate them for the alleged misstatements about Parkay.

Parkay is a line of margarine products in spreadable, sprayable and squeezable forms, and was acquired by ConAgra Foods, the nation’s second largest packaged-food company, in 1998. According to the lawsuit, ConAgra markets Parkay Spray, as a “guilt-free” alternative to traditional butter products, and claims that the product is “0 calories,” “0 fat,” and “fat free” in official product descriptions on company websites and in advertisements.

The lawsuit claims that these representations are false. It alleges that the defendants used unlawful serving sizes to hide the amount of fat and number of calories that a reasonable consumer would actually consume using the product. Such attempts are in direct violation of the Food and Drug Administration’s (FDA) rules, says Steve W. Berman, the Hagens Berman attorney leading the case.

“This cynical scheme is meant to take advantage of consumers who are trying to look out for their health, and the health of their families,” said Mr. Berman. “We plan to show that ConAgra is openly flouting the FDA’s rules and state laws that prohibit the practice of simply lowering the serving size on the label to hide the number of calories in a product.”

The lawsuit also claims that ConAgra failed to follow FDA rules that require disclosing if any ingredients contain fat. Parkay Spray lists “soybean oil” and “buttermilk” in its ingredient list on the label, the complaint alleges, but does not disclose that these ingredients contain fat.