A governmental agency which proposes to operate or continue a food service in a public office building shall first attempt in good faith to make an agreement for the commission for the blind to operate the food service without payment of rent. The governmental agency shall not offer or grant to any other party a contract or concession to operate such food service unless the governmental agency determines in good faith that the commission for the blind is not willing to or cannot satisfactorily provide such food service. This chapter shall not impair any valid contract existing on July 1, 1969, and shall not preclude renegotiation of such contract on the same terms and with the same parties.