Mich. Comp. Laws § 691.1348

Sec. 18. (1) A privilege under section 17 may be waived in a record or orally during a proceeding if it is expressly waived by all parties and, in the case of the privilege of a nonparty participant, it is also expressly waived by the nonparty participant. (2) A person that makes a disclosure or representation about a collaborative law communication that prejudices another person in a proceeding may not assert a privilege under section 17, but this preclusion applies only to the extent necessary for the person prejudiced to respond to the disclosure or representation.