The Social Security Act (the “Act”) requires that all physicians and nonphysician practitioners be uniquely identified for all claims for services that are ordered or referred. A physician or supplier that bills Medicare for a service or item must show the name and unique identifier of the ordering/referring provider on the claim if that service or item was the result of an order or referral. Effective May 23, 2008, the unique identifier must be a National Provider Identifier (NPI). In conjunction with this requirement, the Centers for Medicare & Medicaid Services (CMS) instituted the Provider Enrollment, Chain and Ownership System (PECOS) to better track provider enrollment. PECOS allows providers who bill Medicare to enroll or change their previous enrollment information with CMS.