If there is a valid collective bargaining agreement in effect, no question concerning 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; provided that in the event a valid collective bargaining agreement, together with any renewals or extensions thereof, has been or will be in existence for more than three years, then a question concerning representation may be raised not more than ninety nor less than sixty days prior to the third anniversary date or any subsequent anniversary date of the agreement.