Wash. Rev. Code § 41.59.090
The employee organization 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 employees within the unit without regard to membership in that bargaining representative: PROVIDED, That any employee at any time may present his or her grievance to the employer and have such grievance adjusted without the intervention of the exclusive bargaining representative, as long as such representative has been given an opportunity to be present at that adjustment and to make its views known, and as long as the adjustment is not inconsistent with the terms of a collective bargaining agreement then in effect.
RCW 41.59.090