Nursing assistants, food service workers and support staff at eight Twin Cities hospitals are voting this week on whether to authorize a two- to five-day strike. The vote was called by the Service Employees International Union Healthcare Minnesota, which represents some 3,500 employees who have been in contract talks with the hospitals since January. The union set up voting tables Monday outside three of the affected hospitals: Fairview Southdale, North Memorial Medical Center and Children's Hospital in Minneapolis. The voting, which will continue through Tuesday, also involves workers at Methodist Hospital, Fairview Riverside, Children's in St. Paul, Bethesda Hospital and St. John's Hospital.