Upon receipt of a petition signed by at least ten percent (10%) of the pork producers in North Carolina known to the Association, the Department shall notify the Association, and the Association shall, within six months, conduct a referendum upon the question of continuing the assessment.  If a majority of the votes cast in the referendum are against continuing the assessment, or if the Association fails to conduct a referendum within the six-month period, the assessment expires at the end of the six-month period.  If a majority of the votes cast in the referendum are in favor of continuing the assessment, then no subsequent referendum shall be held for at least three years. (1991, c. 605, s. 1.)