The union representing registered nurses who went on strike Sept. 22 filed a complaint with the National Labor Relations Board that accuses Sutter Health of unlawfully locking out the nurses for four days after the walkout. California Nurses Association-National Nurses United, in charges filed this week, accused the hospital network of retaliating against the nurses and violating their right to strike. Kaiser nurses struck in sympathy that same day with optical and mental health workers, but Kaiser's administration allowed the nurses back the next day. Sutter officials have said they signed a five-day contract with the agency that supplied replacement nurses to fill in for striking employees. The strike took a tragic turn when a cancer patient at Alta Bates Summit Medical Center died because of a medical error by a replacement nurse. The incident remains under investigation.