Mich. Comp. Laws § 450.2422

Sec. 422. A proxy that is entitled "irrevocable proxy", and that states that it is irrevocable, is irrevocable when it is held by any of the following or a nominee of any of the following: (a) In the case of shares or memberships that are transferable, a holder of a pledge or other security interest in the shares or membership. (b) In the case of shares or memberships that are transferable, a person that has purchased or agreed to purchase the shares or membership. (c) A creditor of the corporation that extends or continues credit to the corporation in consideration of the proxy. (d) An individual who has contracted to perform services as a director, officer, or employee of the corporation, if a proxy is required by the contract of employment. (e) A person designated by or under an agreement under section 461. (f) A holder of any other proxy coupled with an interest.