Mich. Comp. Laws § 339.6117

Sec. 1117. (1) An individual who is employed as an apprentice plumber shall register with the department on a form provided by the department not later than 30 days after employment. (2) An apprentice registration is invalid after 5 years from the date of initial registration unless the registered apprentice applies for and takes the examination for journey license. The registration of an apprentice who has applied for a journey license remains valid after the 5-year period until either a license is issued or the apprentice fails to take the examination. (3) On request by the apprentice to the board, the board may grant an extension of an apprentice registration for a period of time as determined appropriate by the board. (4) An apprentice plumber shall, as the apprentice plumber's principal occupation, be engaged in learning and assisting in the installation of plumbing under the direct, on-site, in-person supervision of a journey or master plumber.