WASHINGTON (AP) — A ruling by the Obama administration allowing the sale of gasoline containing 15 percent ethanol is running into legal hurdles from trade groups opposing the plan. The National Petrochemical and Refiners Association sued the Environmental Protection Agency on Monday over the decision to allow the sale of gasoline containing higher blends of corn-based ethanol, the second major group to protest the ruling. The Obama administration said in October that gas stations could start selling the ethanol blend for vehicles built since the 2007 model year, increasing it from the current blend of 10 percent ethanol.