If a metropolitan municipal corporation shall perform the metropolitan transportation function and shall acquire any existing transportation system, it shall assume and observe all existing labor contracts relating to such system and, to the extent necessary for operation of facilities, all of the employees of such acquired transportation system whose duties are necessary to operate efficiently the facilities acquired shall be appointed to comparable positions to those which they held at the time of such transfer, and no employee or retired or pensioned employee of such systems shall be placed in any worse position with respect to pension seniority, wages, sick leave, vacation or other benefits that he or she enjoyed as an employee of such system prior to such acquisition. The metropolitan municipal corporation shall engage in collective bargaining with the duly appointed representatives of any employee labor organization having existing contracts with the acquired transportation system and may enter into labor contracts with such employee labor organization.