Michigan Compiled Laws, Chapter 460. Public Utilities § 460.836

Sec. 36. After the creation of a joint agency, another municipality may become a member of the joint agency upon application to the joint agency after the adoption of a resolution of the governing body of the municipality as prescribed in section 31  1 of this article authorizing the municipality to participate, and with the unanimous consent of the members of the joint agency as provided in section 34(6). 2 A municipality may withdraw from a joint agency, except that all contractual rights acquired and obligations incurred while a member municipality remain in full force and effect.