Mich. Comp. Laws § 15.328

Sec. 8. It is the intention that this act shall constitute the sole law in this state and shall supersede all other acts in respect to conflicts of interest relative to public contracts, involving public servants other than members of the legislature and state officers, including but not limited to section 30 of 1851 PA 156, MCL 46.30. This act does not prohibit a unit of local government from adopting an ordinance or enforcing an existing ordinance relating to conflict of interest in subjects other than public contracts involving public servants.