Wash. Rev. Code § 24.06.220
A plan of merger or consolidation shall be adopted in the following manner:
The board of directors of such corporation shall adopt a resolution approving the proposed plan and directing that it be submitted to a vote at a meeting of members or shareholders which may be either an annual or a special meeting. Written or printed notice or, if specifically permitted by the articles of incorporation or bylaws of the corporation, notice by electronic transmission, setting forth the proposed plan or a summary thereof shall be given to each member and shareholder within the time and in the manner provided in this chapter for the giving of notice of meetings of members and shareholders. The proposed plan shall be adopted upon receiving at least two-thirds of the votes which members and shareholders present in person or by mail or by electronic transmission at each such meeting or represented by proxy are entitled to cast: PROVIDED, That when any class of shares or members is entitled to vote thereon as a class, the proposed amendment must receive at least two-thirds of the votes of the members or shareholders of each class entitled to vote thereon as a class, who are present in person, by mail, by electronic transmission, or represented by proxy at such meeting.
After such approval, and at any time prior to the filing of the articles of merger or consolidation, the merger or consolidation may be abandoned pursuant to provisions therefor, if any, set forth in the plan of merger or consolidation.
RCW 24.06.220