If the employer has reason to doubt the validity of a medical certification, the employer may require the employee to obtain a second opinion, at the employer’s expense, from a health care provider designated by the employer, as long as the health care provider is not employed on a regular basis by the employer and does not regularly contract with the employer. If the first and second opinions differ, the employer may require the employee to obtain a third certification, again at the employer’s expense, from a health care provider chosen or approved by the employer and the employee. The third opinion will be binding. The employer is required to provide the employee with copies of the second and third opinions upon request, within five business days after the request is made.
 29 C.F.R. § 825.307