Mich. Comp. Laws § 120.23

Sec. 23. Each port commission shall have power to sell and convey any property in anywise acquired and owned by the port district whenever the port commission of such district shall have by resolution declared such property to be no longer needed for the purpose of the port district: Provided, That the power herein granted to the commission shall not be exercised without first obtaining the approval therefor by a 2/3 vote of the members elect of the board of supervisors of the county or counties in which such property is located.