Mo. Rev. Stat. § 89.060
Such regulations, restrictions, and boundaries may from time to time be amended, supplemented, changed, modified or repealed. In case, however, of a protest against such change duly signed and acknowledged by the owners of thirty percent or more, either of the areas of the land (exclusive of streets and alleys) included in such proposed change or within an area determined by lines drawn parallel to and one hundred and eighty-five feet distant from the boundaries of the district proposed to be changed, such amendment shall not become effective except by the favorable vote of two-thirds of all the members of the legislative body of such municipality. The provisions of section 89.050 relative to public hearing and official notice shall apply equally to all changes or amendments.
§ 89.060, RSMo