Mich. Comp. Laws § 339.6123

Sec. 1123. An individual who is licensed under this article and employed or acting as a plumbing inspector shall not engage in, or be directly or indirectly connected with, the plumbing business, including, but not limited to, the furnishing of labor, materials, or appliances for the construction, alteration, or maintenance of a building or the preparation of plans or specifications for the construction, alteration, or maintenance of a building, and shall not engage in any work that conflicts with his or her official duties.