Aetna health insurance company is threatening to terminate its contract with North Carolina-based Novant Health on July 1. If the two organizations don't come to an agreement on allowable charges for medical care, about 125,000 Charlotte-area Aetna customers could find themselves out-of-network, and paying more, to use Presbyterian Healthcare services. Aetna sent about 3,000 letters to Presbyterian-affiliated doctors last week, and planned to meet with representatives of its 25 largest employer customers to let them know about the potential contract termination.