An Act amending the act of April 14, 1937 (P. L. 313, No. 87), entitled, as amended, "An act to enable cities of the first, second, and second class A, incorporated towns, boroughs, and townships, to govern and regulate by ordinance the construction, alteration, repairs, ***; and repealing existing laws," providing for referendums in those wards of cities of the second class wherein it is proposed to construct or renovate a building for use as a multi-family dwelling of twenty-five or more units.