Upon the passage of the resolution the city or town clerk shall give twenty days' notice of the pendency of the petition by a written notice posted in three of the most public places in the city or town and a like notice in a conspicuous place on the street or alley sought to be vacated. The said notice shall contain a statement that a petition has been filed to vacate the street or alley described in the notice, together with a statement of the time and place fixed for the hearing of the petition. In all cases where the proceeding is initiated by resolution of the city or town council or similar legislative authority without a petition having been signed by the owners of more than two-thirds of the property abutting upon the part of the street or alley sought to be vacated, in addition to the notice hereinabove required, there shall be given by mail at least fifteen days before the date fixed for the hearing, a similar notice to the owners or reputed owners of all lots, tracts or parcels of land or other property abutting upon any street or alley or any part thereof sought to be vacated, as shown on the rolls of the county treasurer, directed to the address thereon shown: PROVIDED, That if fifty percent of the abutting property owners file written objection to the proposed vacation with the clerk, prior to the time of hearing, the city shall be prohibited from proceeding with the resolution.