(1) A private employer is not liable for any injury received by a third-party occupant of a vehicle that is owned, leased, or rented by the employer if, at the time the injuries were inflicted, the third-party occupant was riding in or on the vehicle with an employee who had explicitly acknowledged in writing the employer's policy on use of vehicles owned, leased, or rented by the employer and the third-party occupant was not:
(a) Specifically and expressly authorized by the employer to be an occupant of the vehicle; or
(b) Acting on behalf of, or for the benefit of, the employer with the knowledge or implied approval or acquiescence of the employer.
(2) For purposes of this section, "third-party occupant" means a person who occupies a vehicle owned, leased, or rented by the private employer and who is not an officer, employee, or agent, or authorized or constructive invitee of the private employer.