The USW, with members at more than 200 refineries, fuel terminals, pipelines and chemical plants across the US, asked workers at Motiva Enterprises LLC's Port Arthur refinery in Texas, the nation's largest, to join a nationwide walkout on Saturday, and issued notices for three other plants to go on strike in 24 hours. This brings the work stoppage - which began on Feb 1 at nine sites from California to Texas and expanded to two BP Plc refineries in the Midwest a week later - to 12 refineries and 3 other facilities.