Mich. Comp. Laws § 124.257

Sec. 7. Any city, village or township, which did not join in the incorporation of an authority, may become a constituent part thereof by amendment to the articles of incorporation adopted by the legislative body of such city, village or township and by the legislative body of each city, village or township of which such authority is composed. Other amendments may be made to such articles of incorporation if adopted by the legislative body of each city, village or township of which the authority is composed. Any such amendment shall be endorsed, published, and certified printed copies filed, in the same manner as the original articles of incorporation, except that the printed copies shall be certified and filed by the recording officer of the authority.