The Center for Medicare & Medicaid Services is investigating whether the University of Minnesota Medical Center, Fairview violated federal law with its billing and collection practices in the emergency room. Officials from the Minnesota Department of Health performed an on-site survey of the Minneapolis hospital over three days last week on behalf of CMS, said Ryan Davenport, a Fairview spokesman. The visit was prompted, Davenport said, by concerns raised in an April report by Attorney General Lori Swanson, who alleged overly aggressive billing and collection tactics on the part of Fairview and a Chicago-based consultant called Accretive Health.