Representatives designated or selected for the purposes of collective bargaining by the majority of the employees in a unit appropriate for such purposes, shall be the exclusive representatives of all the employees in such unit for the purposes of collective bargaining in respect to rates of pay, wages, hours of employment or other conditions of employment, and shall be so recognized by the employer: Provided, That any individual employee at any time may present grievances to his employer and have the grievances adjusted, without intervention of the bargaining representative, if the adjustment is not inconsistent with the terms of a collective bargaining contract or agreement then in effect, if the bargaining representative has been given opportunity to be present at such adjustment.