In the event that medical questions are raised in any case, the Secretary shall have the power to cause the employee to be examined by a physician employed or selected by the Secretary and to obtain from such physician a report containing his estimate of the employee’s physical impairment and such other information as may be appropriate. Any party who is dissatisfied with such report may request a review or reexamination of the employee by one or more different physicians employed or selected by the Secretary. The Secretary shall order such review or reexamination unless he finds that it is clearly unwarranted. Such review or reexamination shall be completed within two weeks from the date ordered unless the Secretary finds that because of extraordinary circumstances a longer period is required. The Secretary shall have the power in his discretion to charge the cost of examination or review under this subsection to the employer, if he is a self-insurer, or to the insurance company which is carrying the risk, in appropriate cases, or to the special fund in section
944 of this title.