A shareholder lawsuit filed against Community Health Systems here seeks to recoup stock losses suffered after the hospital chain's admissions policies and Medicare payments were called into question in a takeover battle with a rival chain. The suit, which was filed in federal court, contends that Community Health failed to provide shareholders with "material" information about how the hospital chain is run and how it handles certain billings. Community's stock price plunged early last month after rival Tenet Healthcare alleged that the Franklin-based healthcare company encourages medically unnecessary admissions to boost payments from Medicare, according to the suit filed on behalf of Norfolk Retirement System pension fund. In early April, Community Health's stock was trading near $41 per share, but it dropped as low as $25.81 after the Tenet flap surfaced. Shares have since rebounded somewhat, closing Tuesday at $30.90 per share in New York Stock Exchange trading.