Michigan Compiled Laws, Chapter 339. Occupational Code § 339.6125

Sec. 1125. (1) A governmental subdivision may not exempt itself from the licensing requirements of this article and may not engage in or require local licensing.

(2) Except as otherwise provided in subsections (3) and (6) and section 1107,  1 the state or a governmental subdivision shall issue a plumbing permit only to a licensed plumbing contractor. The state or a governmental subdivision shall require the plumbing contractor to record his or her current plumbing contractor license number on the permit application. A licensed plumbing contractor shall designate 1 or more licensed master plumbers who are employed full-time who directly supervise the installation of plumbing to obtain permits using the license number of the plumbing contractor. The master plumber's license number must also be recorded on the permit application.

(3) In those instances where business or industrial procedure requires the regular employment of a full-time licensed master plumber, a licensed master plumber is authorized to secure permits for installations of plumbing on the premises owned or occupied and used by the business provided the licensed master plumber physically supervises the plumbing work and represents only the business or industrial employer. The employer and the licensed master plumber shall sign an annual affidavit, furnished by the department, and the affidavit shall be provided to and kept on file by the department. The department shall determine the filing fee for an affidavit. A new affidavit must be filed before permits will be issued if the licensed master plumber's employment is terminated. The affidavit shall contain the following:

(4) A plumbing contractor who is licensed under this article who performs work in a governmental subdivision shall register his or her license with the enforcing agency that issues permits and provides inspection services if required by the enforcing agency. The registration is valid until the expiration date of the plumbing contractor license. Each governmental subdivision in this state must grant registration to a plumbing contractor who is licensed under this article if a fee, in an amount determined by the governmental subdivision and that does not exceed $15.00, is paid to the governmental subdivision.

(5) Master plumbers, journey plumbers, and apprentice plumbers shall carry their licenses and a form of identification that includes his or her photograph. If requested by an enforcing agency, a licensee or apprentice registrant shall present his or her license or registration and a form of identification that includes his or her photograph.

(6) If the plumbing, reconstruction, alteration, or repair of pipes, tanks, or fixtures is performed without compensation by an individual who is licensed under this article for or on behalf of a charitable organization, the owner of the property on which the work is performed may obtain the permit required under subsection (2). This subsection applies only to the reconstruction, renovation, or remodeling of a 1-family to 4-family dwelling.