24 Pa. Stat. § 791.13
The Commonwealth does hereby pledge to, and agree with, any person, firm or corporation or Federal agency subscribing to, or acquiring, the bonds to be issued by the Authority for the construction, financing, extension, improvement, or enlargement of any project, or part thereof, or for refunding purposes, that the Commonwealth will not limit or alter the rights hereby vested in the Authority, or limit or alter any provisions for the security and protection of the Authority and its bondholders contained in this act or as now provided by law, until all bonds at any time issued, together with the interest thereon, are fully met and discharged. The Commonwealth does further pledge to and agree with the United States and any other Federal agency that, in the event that any Federal agency shall construct or contribute any funds for the construction, financing, extension, improvement or enlargement of any project or any portion thereof, the Commonwealth will not alter or limit the rights and powers of the Authority in any manner which would be inconsistent with the continued maintenance and operation of the project, or the improvement thereof, or which would be inconsistent with the due performance of any agreements between the Authority and any such Federal agency, and the Authority shall continue to have and may exercise all powers herein granted so long as the same shall be necessary or desirable for the carrying out of the purposes of this act and the purposes of the United States in the construction or improvement or enlargement of any project or such portion thereof.
24 P.S. § 791.13