Wash. Rev. Code § 35.22.350
Every city of the first class which owns and operates a waterworks system, a light and power system, a street railway or other public utility, shall have power, through its proper officers, to deal with and to enter into contracts for periods not exceeding one year with its employees engaged in the construction, maintenance, or operation thereof through the accredited representatives of the employees including any labor organization or organizations authorized to act for them concerning wages, hours and conditions of labor in such employment, and every city having not less than one hundred forty thousand nor more than one hundred and seventy thousand population is empowered and authorized to immediately place in effect any adjustment or change in such wages, hours and conditions of labor of such employees as may be required to conform to the provisions of any such contract, irrespective of the provisions of any annual budget or act relating thereto: PROVIDED, That not more than one such contract not in conformity with any annual budget shall be made during any budget year, nor shall any such adjustment or change be made which would result in an excess of expenditures over revenues of such public utility.
RCW 35.22.350
Labor regulations: Title 49 RCW.