The regulations, restrictions, and boundaries set forth in this ordinance may from time to time be amended, supplemented, changed, or repealed, provided however that no such action may be taken until after a public hearing in relation thereto, at which parties in interest and citizens shall have an opportunity to be heard. At least 15 days’ notice of the time and place of such hearing shall be published in a newspaper of general circulation in the city.

When a proposed amendment affects the zoning classification of property, and in case a protest against such change is signed by the owners of 20 percent or more either of the area of the lots included in such proposed change, or of those immediately adjacent in the rear thereof extending 1000 feet therefrom, or of those directly opposite thereto, extending 1000 feet from the street frontage of such opposite lots, then such amendments shall not become effective except by the favorable vote of 80 percent of the City Council.