These regulations, restrictions and boundaries may, from time to time, be amended, supplemented, changed, modified or repealed. In case, however, of a written protest against a change or repeal which is filed with the Clerk and signed by the owners of twenty percent or more of the area of the lots included in the proposed change or repeal, or by the owners of twenty percent or more of the property which is located within two hundred feet of the external boundaries of the property for which the change or repeal is proposed, the change or repeal shall not become effective except by the favorable vote of at least three-fourths of all the members of the Council. All requests for amendments, unless initiated by the Planning and Zoning Commission or the Council, shall be filed with the Zoning Administrator. Prior to taking action on any such amendment, the Council shall refer said amendment to the Planning and Zoning Commission and shall afford the Commission the opportunity to make recommendations thereon. The Council shall provide for the manner in which the regulations and restrictions and the boundaries of the districts shall be determined, established and enforced and from time to time amended, supplemented or changed. However, the regulation, restriction or boundary shall not become effective until after a public hearing, at which parties in interest and citizens shall have an opportunity to be heard. The notice of the time and place of the hearing shall be published as provided in Section 362.3, Code of Iowa, except that at least seven days notice must be given and in no case shall the public hearing be held earlier than the next regularly scheduled Council meeting following the published notice.