The regulations imposed and the districts created under this Article may be amended from time to time by the township board by ordinance or resolution after the ordinance or resolution establishing the regulation has gone into effect, but no amendments shall be made without a hearing before the board of appeals. At least 15 days notice of the time and place of the hearing shall be published in an official paper or a paper of general circulation in the township. If there is a written protest against any proposed amendment, signed and acknowledged (i) by the owners of 20% of the frontage proposed to be altered, (ii) by the owners of 20% of the frontage immediately adjoining or across an alley from the frontage proposed to be altered, or (iii) by the owners of 20% of the frontage directly opposite the frontage proposed to be altered, the amendment shall not be passed except by the favorable vote of three-fourths of all the members of the township board.