Wash. Rev. Code § 41.56.080
The bargaining representative which has been determined to represent a majority of the employees in a bargaining unit shall be certified by the commission as the exclusive bargaining representative of, and shall be required to represent, all the public employees within the unit without regard to membership in said bargaining representative: PROVIDED, That any public employee at any time may present his or her grievance to the public employer and have such grievance adjusted without the intervention of the exclusive bargaining representative, if the adjustment is not inconsistent with the terms of a collective bargaining agreement then in effect, and if the exclusive bargaining representative has been given reasonable opportunity to be present at any initial meeting called for the resolution of such grievance.
RCW 41.56.080