(a) Local Acts of the General Assembly proposing annexation of any area comprised of more than 50 percent by acreage of property used for residential purposes shall be adopted pursuant to the procedures of this article.

(b) The author of such legislation shall provide notice to the governing authority of the county as required by Code Section 36-36-6. Such bill may include a requirement for referendum approval of the annexation under such terms and conditions as specified in such local law; provided, however, if the number of residents in the area to be annexed exceeds 3 percent of the population of the municipal corporation or 500 people, whichever is less, as determined by the most recent United States decennial census, referendum approval shall be required in the area to be annexed. The cost of holding the referendum required by this article shall be paid from funds of the municipality proposing the annexation.