Wash. Rev. Code § 67.08.200
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 department charging a license holder or applicant with unprofessional conduct and specifying the grounds for the complaint. If the department determines that the complaint merits investigation or if the department has reason to believe, without a formal complaint, that a license holder or applicant may have engaged in unprofessional conduct, the department 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 any civil action related to the filing or contents of the complaint.
RCW 67.08.200