The state NAACP and other groups representing low-income and working families on Tuesday called on Carolinas HealthCare System to stop suing patients who can’t afford to pay their hospital bills. Their plea came in response to an investigation by the Charlotte Observer and The (Raleigh) News & Observer, which last week revealed that the nonprofit hospital chain has filed more than 12,000 bill-collection lawsuits in the five years ending in 2010. Other groups calling for change include the N.C. Justice Center, Action NC, the N.C. AFL-CIO, and the Black Women's Caucus. The groups also demanded that Carolinas HealthCare remove the liens it currently holds on the primary residences of former patients.