In implementing an ACA provision requiring physicians to enroll in Medicare to certify or order services for Medicare beneficiaries, CMS has discovered unique enrollment issues for certain types of physicians and practitioners that typically do not send claims to Medicare contractors for their services. Consequently, CMS has modified the enrollment process to accommodate the special circumstances of physicians employed by the Department of Veterans Affairs, the Public Health Service, the Department of Defense Tricare program, federally qualified health centers, rural health clinics, or critical access hospitals, along with physicians in a fellowship and dentists.