Electricity companies Big Brown Power Co. and Luminant Generation Co. petitioned the U.S. Court of Appeals for the Fifth Circuit on July 31, challenging an Environmental Protection Agency notice that said that two North Texas coal plants owned by the firms violated Texas prevention of significant deterioration regulations. The notice, dated July 11, charges that Luminant and Big Brown failed to obtain required PSD permits before completing recent physical and operating changes, which led to significant net increases in nitrogen oxide and sulfur dioxide emissions.