Wash. Rev. Code § 18.74.135
This chapter shall not be construed to restrict the ability of any insurance entity regulated by Title 48 RCW, or any state agency or program from limiting or controlling the utilization of physical therapy services by the use of any type of gatekeeper function; nor shall it be construed to require or prohibit that individual or group policies or contracts of an insurance carrier, health care service contractor, or health maintenance organization provide benefits or coverage for services and supplies provided by a person licensed under this chapter. For the purpose of this chapter, "gatekeeper function" means any provision in a contract which establishes a threshold requirement, such as a recommendation from a case manager or a primary care provider, which must be satisfied before a covered person is eligible to receive benefits under the contract.
RCW 18.74.135