53 Pa. C.S. § 8112
Except as otherwise specified in this subpart, a local government unit may enter into and perform contracts with the holders of its bonds or notes binding upon the original purchasers and their respective transferees placing greater reasonable and lawful restrictions on the local government unit or on the action of individual holders of bonds or notes than are provided in this subpart, but no additional agreement restricting the action of a holder of a bond or note shall be binding upon a remote holder of a bond or note unless the substance of the agreement is set forth in the text of the bond or note, or set forth in a bond resolution or indenture of trust which is kept available in one or more designated public offices and to all of which a reference is made in the text of the bond or note.
53 Pa.C.S. § 8112