53 Pa. Stat. § 881.413
Any municipality which has joined the system under the provisions of this Article IV may, with the approval of the board, amend the contract with the board to increase any of the benefits enumerated in Article IV to its members. The board shall not enter into any amended contract with any municipality which decreases benefits, nor shall it enter into any amended contract with a municipality which provides for benefits in excess of or minimum member's contribution rates less than those available to it under any other existing law pertaining to the establishment of retirement systems for that class of municipality except to the extent that excess investment earnings are allocated to provide for additional pension benefits or members accruals as otherwise provided in this law. Before the board approves any such amended contract it shall first determine, through its actuary, that the plan outlined is actuarially sound. Any member municipality which elects to enter into an amended contract for increased benefits which would result in an increase in its employes contribution rates shall first obtain the written consent of at least seventy-five per cent of its then member employes. Additional costs for increases in benefits shall become the responsibility of the municipality and/or the member as specified in the contract.
53 P.S. § 881.413