A public utility district that has or had a license from the federal power commission to construct a hydroelectric project of an estimated cost of more than two hundred fifty million dollars, including interest during construction, or has a population of five hundred thousand or more, shall be classified as a five commissioner district if voters of the district approve a ballot proposition authorizing the change. In submitting the question to the voters for their approval or rejection, the proposition shall be expressed on the ballot in substantially the following terms:

Should a majority of the voters voting on the question approve the proposition, the district shall be declared a five commissioner district upon the certification of the election returns.