Whenever, under the provisions of this subchapter, the Secretary is required to determine the approval or disapproval of producers, the Secretary shall consider the approval or disapproval by any cooperative association of producers, engaged in a bona fide manner in marketing milk or the products thereof, as the approval or disapproval of the producers who are members of or under contract with such cooperative association of producers. If a cooperative association of producers elects to vote on behalf of its members, such cooperative association shall provide each producer, on whose behalf the cooperative association is expressing approval or disapproval, a description of the question presented in the referendum together with a statement of the manner in which the cooperative association intends to cast its vote on behalf of the membership. Such information shall inform the producer of procedures to follow to cast an individual ballot should the producer so choose within the period of time established by the Secretary for casting ballots. Such notification shall be made at least thirty days prior to the referendum and shall include an official ballot. The ballots shall be tabulated by the Secretary and the vote of the cooperative association shall be adjusted to reflect such individual votes.