Washington Revised Code Title 44. State Government--Legislative § 44.90.045. Commission authority--Interference with the legislature's core function prohibited

(1) As provided by this chapter, the commission or the court shall determine all questions described by this chapter as under the commission's authority. However, such authority may not result in an order or rule that intrudes upon or interferes with the legislature's core function of efficient and effective law making or the essential operation of the legislature, including that an order or rule may not:

(2) No member of the legislature may be compelled by subpoena or other means to attend a proceeding related to matters covered by this chapter during a legislative session, committee assembly days, or for 15 days before commencement of each session.