Wash. Rev. Code § 18.39.420
A person, including but not limited to a consumer, licensee, corporation, organization, and state and local governmental agency, may submit a written complaint to the board charging a license, registration, endorsement, or permit holder or applicant with unprofessional conduct and specifying the grounds for the complaint. If the board determines that the complaint merits investigation, or if the board has reason to believe, without a formal complaint, that a license holder or applicant might have engaged in unprofessional conduct, the board shall investigate to determine whether there has been unprofessional conduct. A person who files a complaint under this section in good faith is immune from suit in a civil action related to the filing or contents of the complaint.
RCW 18.39.420