The nation’s largest hospital chain, Columbia/HCA Healthcare Corp., has reached a tentative agreement to pay the federal government $745 million as a partial settlement of a massive billing fraud investigation. The Justice Department stated, however, that it has not settled all the issues it has been investigating, and that it will be seeking more money from the hospital giant.

Columbia/HCA has been under investigation for at least three years, after whistleblowers alleged that the company was submitting false claims to Medicare and Medicaid. Industry analysts estimate the overall settlement to exceed $1 billion.