(a) Review.--Every five years the secretary shall call a referendum of affected producers within each agricultural commodity group for which a marketing program exists to determine whether or not a majority of those voting still desire a marketing program.

(b) Referendum on amendments.--The secretary shall call for a referendum on amendments to a marketing program within a reasonable period of time, upon the request of the advisory board or with written request of 10% of the producers in a commodity group of over 2,000 affected producers or 15% of the producers in a commodity group of less than 2,000 affected producers. In voting on an amendment to the marketing program, the vote shall be only on the amendment and shall not terminate the program.