Wash. Rev. Code § 81.28.230
Whenever the commission finds, after a hearing had upon its own motion or upon complaint, as provided in this chapter, that the rates, fares, or charges demanded, exacted, charged, or collected by any common carrier subject to regulation by the commission as to rates and service for the transportation of persons or property within the state or in connection therewith, or that the regulations or practices of the common carrier affecting those rates are unjust, unreasonable, unjustly discriminatory, or unduly preferential, or in any way are in violation of the provisions of law, or that the rates, fares, or charges are insufficient to yield a reasonable compensation for the service rendered, the commission shall determine and fix by order the just, reasonable, or sufficient rates, fares, or charges, or the regulations or practices to be thereafter observed and enforced.
RCW 81.28.230