Wash. Rev. Code § 41.80.320
(1) Within ten working days after the first Monday in September of every odd-numbered year, the state's bargaining representative and the exclusive bargaining representative for the appropriate bargaining unit shall attempt to agree on an interest arbitration panel consisting of three members to be used if the parties are not successful in negotiating a comprehensive collective bargaining agreement. Each party shall name one person to serve as its arbitrator on the arbitration panel. The two members so appointed shall meet within seven days following the appointment of the later appointed member to attempt to choose a third member to act as the neutral chair of the arbitration panel. Upon the failure of the arbitrators to select a neutral chair within seven days, the two appointed members shall use one of the two following options in the appointment of the third member, who shall act as chair of the panel:
(5) Except as provided in this subsection, the written determination shall be final and binding upon both parties.
[ 2019 c 234 s 5.]