5 USC 8103 - Medical services and initial medical and other benefits

(a) The United States shall furnish to an employee who is injured while in the performance of duty, the services, appliances, and supplies prescribed or recommended by a qualified physician, which the Secretary of Labor considers likely to cure, give relief, reduce the degree or the period of disability, or aid in lessening the amount of the monthly compensation. These services, appliances, and supplies shall be furnished
(1) whether or not disability has arisen;
(2) 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
(3) by or on the order of United States medical officers and hospitals, or, at the employees option, by or on the order of physicians and hospitals designated or approved by the Secretary.

The employee may initially select a physician to provide medical services, appliances, and supplies, in accordance with such regulations and instructions as the Secretary considers necessary, and may be furnished necessary and reasonable transportation and expenses incident to the securing of such services, appliances, and supplies. These expenses, when authorized or approved by the Secretary, shall be paid from the Employees Compensation Fund.

(b) 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.