Wash. Rev. Code § 41.80.070
(1) A bargaining unit of employees covered by this chapter existing on June 13, 2002, shall be considered an appropriate unit, unless the unit does not meet the requirements of (a) and (b) of this subsection. The commission, after hearing upon reasonable notice to all interested parties, shall decide, in each application for certification as an exclusive bargaining representative, the unit appropriate for certification. In determining the new units or modifications of existing units, the commission shall consider: The duties, skills, and working conditions of the employees; the history of collective bargaining; the extent of organization among the employees; the desires of the employees; and the avoidance of excessive fragmentation. However, a unit is not appropriate if it includes:
[ 2002 c 354 s 308.]