Mich. Comp. Laws § 570.589

Sec. 9. A written demand on behalf of the owner of commercial real estate may be served on a person claiming a commercial real estate broker's lien, demanding that an action be commenced to enforce the lien or that an answer be filed in an action pending between the owner and the lien claimant. If the action is not commenced or the answer is not filed within 30 days after service of the demand, the lien is extinguished without further action. Service of the demand may be by registered or certified mail, return receipt requested, or by personal service.