Wis. Stat. § 145.04: Water and sewerage systems.

(1) Ordinance rules. A 1st, 2nd or 3rd class city with a water system or sewerage system shall, and a village, 4th class city, town, county or metropolitan sewerage commission may, by ordinance, prescribe rules relating to local permits for the installation, alteration and inspection of plumbing to safeguard the public health.

(2) No local licenses. No city, village, town, town sanitary district, county, metropolitan sewerage district commission or other agency may require the licensing of any person licensed or registered under this chapter or prohibit the person from engaging in or working at business within the scope of the person’s license or permit.

(3) Reports to department. The authorities of any such city or metropolitan sewerage district shall report to the department each failure on the part of a state licensed plumber to qualify as a journeyman or master plumber and each willful violation of any plumbing regulation.