Mich. Comp. Laws § 767.19

Sec. 19. Members of the grand jury may be required by any court to testify, whether the testimony of a witness examined before such jury is consistent with, or different from the evidence given by such witness before such court; and they may also be required to disclose the testimony given before them by any person, upon complaint against such person for perjury, or upon his trial for such offense; but in no case can a member of a grand jury be obliged or allowed to testify or declare in what manner he or any other member of the jury voted on any question before them, or what opinions were expressed by any juror in relation to any such question.