Phil Ochs is seeking class-action status for the lawsuit, which was filed in Ford County District Court. It alleges that the co-op bought large quantities of cheese from the Chicago Mercantile Exchange in an attempt to manipulate the market.
The class would be all Kansans who bought dairy products from Kansas retailers between April 1, 2004, and the present.
The Chicago Mercantile Exchange is the primary market for spot prices for dairy products.
Last month the dairy group and two former executives agreed to pay a $12 million fine under a settlement agreement with the Commodity Futures Trading Commission. The panel was investigating the cooperative's trading activities on the Chicago Mercantile Exchange in 2004.