A coalition of Texas cities has filed suit against the state Commission on Environmental Quality, charging that it violated state law by approving air-emission permits to build two TXU Energy coal-fired generating units at Oak Grove power station near Waco, with a combined capacity of about 1,600 MW. Dallas, Fort Worth, Houston, El Paso and Travis County near Austin, say the commission ignored earlier legal opinions against granting the permit because TXU had not proven that its technology was the best available to control nitrous oxides and mercury emissions.