Nurses at 16 hospitals in the Twin Cities and Duluth areas have authorized workers to go on a second strike, which union leaders say will begin on Dec. 11 if a contract deal is not reached in coming days. The Minnesota Nurses Association said the walkouts will last until Dec. 31 at most hospitals; nurses at St. Luke’s hospitals in Duluth and Two Harbors will stay on strike until a deal is reached. Leaders of the association hope the vote will motivate hospital leadership to improve offers on pay, workplace violence prevention and staffing levels. Allina Health is one of the hospital systems involved, and says it is disappointed but negotiations will continue.