Where there is a valid collective bargaining agreement in effect, no question of representation may be raised except during the period not more than ninety nor less than sixty days prior to the expiration date of the agreement. In the event that a valid collective bargaining agreement, together with any renewals or extensions thereof, has been or will be in existence for three years, then the question of representation may be raised not more than ninety nor less than sixty days prior to the third anniversary date of the agreement or any renewals or extensions thereof as long as such renewals and extensions do not exceed three years.