The qualified industry organizations may conduct, at their own expense, a referendum among producers and retail marketers for the creation of a Propane Education and Research Council. The Council, if established, shall reimburse the qualified industry organizations for the cost of the referendum accounting and documentation. Such referendum shall be conducted by an independent auditing firm agreed to by the qualified industry organizations. Voting rights in such referendum shall be based on the volume of propane produced or odorized propane sold in the previous calendar year or other representative period. Upon approval of those persons representing two-thirds of the total volume of propane voted in the retail marketer class and two-thirds of all propane voted in the producer class, the Council shall be established, and shall be authorized to levy an assessment on odorized propane in accordance with section 6405 of this title. All persons voting in the referendum shall certify to the independent auditing firm the volume of propane represented by their vote.