The City shall not negotiate nor make any collective bargaining agreement or contract with any of the employees working in classifications covered herein individually or collectively. Any agreements entered into between the City and employees covered herein shall be through the President of the Local or representa tive(s) authorized by the President of the Local. Any other agreements shall be of no effect. All side agreements and memoranda of understanding shall be signed by the President of the Local and a responsible steward for the unit.