Mich. Comp. Laws § 38.1642b

Sec. 42b. (1) A qualified participant is immediately 100% vested in his or her contributions made to Tier 2. (2) A qualified participant who is a member of Tier 1 vests in the employer contributions made on his or her behalf to Tier 2 according to the following schedule: (a) On completion of 2 years of service, 50%. (b) On completion of 3 years of service, 75%. (c) On completion of 4 years of service, 100%.