53 Pa. Stat. § 1001
All stationery, printing, paper and fuel used in the councils, and in other departments of the city government, and all work and materials required by the city, shall be furnished, and the printing and all other kinds of work to be done for the city, shall be performed under contract to be given to the lowest responsible bidder, under such regulations as shall be prescribed by ordinance; and it shall be the duty of councils forthwith to enact such ordinances; no member or officer of councils, or any department of the city governments, shall be in any way interested in such contracts, directly or indirectly, either at its inception or during the progress of its fulfillment, or furnish any materials or supplies or labor for such contracts.
53 P.S. § 1001