Wash. Rev. Code § 49.66.060
No employee organization, bargaining representative, person, or employee shall authorize, sanction, engage in, or participate in a strike (including but not limited to a concerted work stoppage of any kind, concerted slowdown or concerted refusal or failure to report for work or perform work) or picketing against an employer under any circumstances, whether arising out of a recognition dispute, bargaining impasse, or otherwise: PROVIDED, That nothing in this section shall prohibit picketing or other publicity for the sole purpose of truthfully advising the public of the existence of a dispute with the employer, unless an effect of such picketing or other publicity is (a) to induce any employee of the employer or any other individual, in the course of his or her employment, not to pick up, deliver, or transfer goods, not to enter the employer's premises, or not to perform services; or (b) to induce such an employee or individual to engage in a strike.
RCW 49.66.060