Wash. Rev. Code § 18.165.180
A person, including but not limited to consumers, licensees, corporations, organizations, and state and local governmental agencies, may submit a written complaint to the department charging a license holder or applicant with unprofessional or unlawful conduct and specifying the grounds for the charge. If the director determines that the complaint merits investigation, or if the director has reason to believe, without a formal complaint, that a license holder or applicant may have engaged in unprofessional or unlawful conduct, the director shall investigate to determine if there has been unprofessional or unlawful 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 18.165.180