53 Pa. Stat. § 16083
The city controller shall have power to enter into such agreements, as he may deem necessary, to assure the payment of delinquent taxes by persons having claims or accounts against the city, including therein provision for the application of moneys due by the city on any such claim or account to the payment of such delinquent taxes, and the satisfaction of such taxes on the public records, in whole or in part. If any person shall, upon demand of the city controller, refuse to enter into any such agreement, the city controller shall have power to continue to further withhold his approval of the payment of such claim or account against the city, or any part thereof, and advise such person that the city has a set-off against his claim or account, or the part thereof not approved, for delinquent taxes, and that payment thereof will be refused until such delinquent taxes are paid or provision for their payment made.
53 P.S. § 16083