Wash. Rev. Code § 29A.32.280
For each measure from a unit of local government that is included in a local voters' pamphlet, the legislative authority of that jurisdiction shall, not later than the resolution deadline, formally appoint a committee to prepare arguments advocating voters' approval of the measure and shall formally appoint a committee to prepare arguments advocating voters' rejection of the measure. The authority shall appoint persons known to favor the measure to serve on the committee advocating approval and shall, whenever possible, appoint persons known to oppose the measure to serve on the committee advocating rejection. Each committee shall have not more than three members, however, a committee may seek the advice of any person or persons. If the legislative authority of a unit of local government fails to make such appointments by the prescribed deadline, the county auditor shall whenever possible make the appointments.
RCW 29A.32.280