Unless a proposed amendment, supplement or change has been approved by the planning commission, or if a protest against such proposed amendment, supplement or change has been filed with the city secretary, duly signed and acknowledged by the owners of twenty (20) percent or more, either of the area of the lots included in such a proposed change or those immediately adjacent or adjoining thereof extending two hundred (200) feet therefrom or of those directly opposite thereto extending two hundred (200) feet from the street frontage of such opposite lots, such amendment shall not become effective except by a three-fourths vote of the governing body.