A local improvement may be ordered only by an ordinance of the city or town council, pursuant to either a resolution or petition therefor. The ordinance must receive the affirmative vote of at least a majority of the members of the council.
Charters of cities of the first class may prescribe further limitations. In cities and towns other than cities of the first class, the ordinance must receive the affirmative vote of at least two-thirds of the members of the council if, prior to its passage, written objections to its enactment are filed with the city clerk by or on behalf of the owners of a majority of the lineal frontage of the improvement and of the area within the limits of the proposed improvement district.
RCW 35.43.070