Any employee or group of employees may at any time, either individually or through a representative of their own choosing, present grievances to the employer and have such grievances adjusted, without the intervention of the exclusive representative; provided, the adjustment is reached prior to arbitration pursuant to Section 3589, and the adjustment is not inconsistent with the terms of a written memorandum then in effect. The employer shall not agree to resolution of the grievance until the exclusive representative has received a copy of the grievance and the proposed resolution, and has been given the opportunity to file a response.