53 Pa. Stat. § 4595
No person other than a registered master plumber, as herein provided, shall be allowed to carry on, or engage in, the business, nor shall any person or persons expose the sign of plumbing, house or building drainage, or any advertisement or display pertaining thereto (wholesale show rooms excepted), unless he or they have first secured a license or certificate and been registered in the office of the board or bureau of health of such cities, or in the case of a borough, incorporated town or township of the first class, then register with a board or bureau of health of such municipality, if any functioning, and if none such, then with the Department of Health of the Commonwealth; nor shall any person or persons other than a registered master plumber, or a registered journeyman plumber in his or their employ (registered apprentices excepted) be allowed to alter, repair, or make any connection with, any drain, soil, waste, or vent-pipe, or any pipe connected therewith, or to repair, or alter the location of any waterpipe.
53 P.S. § 4595