If the commission elects to conduct an election to ascertain the exclusive bargaining representative, and upon the request of a prospective bargaining representative showing written proof of at least thirty percent representation of the symphony musicians within the unit, the commission shall hold an election by secret ballot to determine the issue. The ballot shall contain the name of the bargaining representative and of any other bargaining representative showing written proof of at least ten percent representation of the symphony musicians within the unit, together with a choice for any symphony musician to designate that he or she does not desire to be represented by any bargaining agent. Where more than one organization is on the ballot and neither of the three or more choices receives a majority vote of valid ballots cast, a runoff election shall be held. The runoff ballot shall contain the two choices which received the largest and second-largest number of votes. No question concerning representation may be raised within one year of a certification or attempted certification. 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. Any agreement which contains a provision for automatic renewal or extension of the agreement shall not be a valid agreement; nor shall any agreement be valid if it provides for a term of existence for more than three years.