United States Sugar Corp., a Clewiston, Florida, company that markets sugar cooperatively with Red River Valley sugarbeet growers, is seeking to purchase Imperial Sugar Co., including a major refinery in the Savannah, Georgia, area. The U.S. Department of Justice on Tuesday, Nov. 23, announced it was suing to block the purchase that could increase the market share of United Sugars Corp., the Edina, Minn.-based co-op marketing company, from its current 25% market share, to 32% to 34%.