By mutual agreement, the parties may waive mediation and proceed with binding arbitration as provided for in the impasse procedures agreed to under RCW 47.64.200
or in 47.64.300 through 47.64.320
, as applicable. The waiver shall be in writing and be signed by the representatives of the parties. Regardless of the status of mediation, the parties must comply with the interest arbitration agreement under RCW 47.64.170
(6)(a), absent any subsequent agreement to the contrary.