No amendment of this ordinance shall be made without a hearing before a commission or committee designated by the village board. At least fifteen (15) days' notice of the time and place of such hearing shall be published in a paper of general circulation within the village. In case of written protest against any proposed amendment, signed and acknowledged by the owners of twenty (20) percent of the frontage proposed to be altered, or by the owners of twenty (20) percent of the frontage immediately adjoining or across an alley therefrom, or by the owners of twenty (20) percent of the frontage directly opposite the frontage proposed to be altered as such regulations or district, filed with the village clerk, such amendment shall not be passed except by the favorable vote of two thirds of all of the members of the village board.