5 U.S.C. § 8103: Medical services and initial medical and other benefits

whether or not disability has arisen; notwithstanding that the employee has accepted or is entitled to receive benefits under subchapter III of chapter 83 of this title or another retirement system for employees of the Government; and by or on the order of United States medical officers and hospitals, or, at the employee’s option, by or on the order of physicians and hospitals designated or approved by the Secretary. The Secretary, under such limitations or conditions as he considers necessary, may authorize the employing agencies to provide for the initial furnishing of medical and other benefits under this section. The Secretary may certify vouchers for these expenses out of the Employees’ Compensation Fund when the immediate superior of the employee certifies that the expense was incurred in respect to an injury which was accepted by the employing agency as probably compensable under this subchapter. The Secretary shall prescribe the form and content of the certificate. an employee or individual not within the definition of ‘employee’ in section 8101(1)(A), (B), or (D) of title 5, United States Code; a member of the Metropolitan Police or the Fire Department of the District of Columbia who is pensioned or pensionable under sections 521—535 of title 4, District of Columbia Code; or a member of a uniformed service.”