Michigan Compiled Laws, Chapter 38. Civil Service and Retirement § 38.17a

Sec. 17a. (1) If an employee of a department of a governmental unit of the state is transferred to the employ of the state, by reason of a function or functions of the department being transferred to the state, the employee so transferred, who does not withdraw his accumulated contributions from the governmental unit's retirement system, and subsequent to the date of his transfer acquires at least 1 year of service credit as a member of the state employees' retirement system, shall be entitled to use the credited service in force previously acquired as a member of the governmental unit's retirement system in meeting the service requirements for all retirement allowances and death benefits by the state employees' retirement system. The credited service acquired in the employ of the governmental unit shall not be used in computing the amount of a retirement allowance to be paid by the state employees' retirement system.

(2) For the purposes of this act “governmental unit of the state” includes the international bridge authority created by Act No. 99 of the Public Acts of 1954, being sections 254.221 to 254.240 of the Michigan Compiled Laws.