Mich. Comp. Laws § 450.1422

Sec. 422. A proxy which is entitled "irrevocable proxy", and which 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) A pledgee of or other holder of a security interest in the shares. (b) A person who has purchased or agreed to purchase the shares. (c) A creditor of the corporation who extends or continues credit to the corporation in consideration of the proxy. (d) A person 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.