In case of a protest against such amendment, change, modification or repeal, signed by the owners of 20% or more either of the area or the lots included in such proposed changes or of those immediately adjacent in the rear thereof extending 100 feet therefrom, or of those directly opposite thereto, extending 100 feet from the street frontage of such opposite lots, such amendment, supplement, change or modification shall not become effective except by the favorable vote of 2/3 of all the members of the governing body.