A surge of antitrust class actions in Chicago federal court accuse the largest producers of frozen- potato products of overcharging consumers, grocery outlets and restaurants for popular appetizers and profiting handsomely from anticompetitive conduct in violation of the Sherman Act.

At least 12 complaints filed in the U.S. District Court for the Northern District of Illinois since Nov. 15 allege Lamb Weston, McCain Foods, J.R. Simplot Co. and Cavendish Farms have conspired to inflate the price of french fries, hash browns and tater tots sold in the $68 billion annual U.S. market for frozen potato products.