77 Pa. Stat. § 441
All contracts executed by the Commonwealth of Pennsylvania, or any officer or bureau or department thereof, on behalf of the said Commonwealth, or by any municipality, or any officer or bureau or board thereof, or by any municipal division or subdivision of the Commonwealth, which contracts shall involve the construction or doing of any work involving the employment of labor, shall contain a provision that the contractor shall accept, in so far as the work covered by any such contract is concerned, the provisions of the Workmen's Compensation Act of 1915, and any supplements or amendments thereto which may hereafter be passed, and that the said contractor will insure his liability thereunder, or file with the Commonwealth, or the municipal corporation or board with whom the contract is made, a certificate of exemption from insurance from the Bureau of Workmen's Compensation of the Department of Labor and Industry.
77 P.S. § 441