Wash. Rev. Code § 48.21A.030
Notwithstanding any other provision of this code or any other law which may be inconsistent herewith, any insurer may join with one or more other insurers, to plan, develop, underwrite, and offer and provide to any person who is sixty-five years of age or older and to the spouse of such person, extended health insurance against financial loss from accident or disease, or both. Such insurance may be offered, issued and administered jointly by two or more insurers by a group policy issued to a policyholder through an association formed for the purpose of offering, selling, issuing and administering such insurance. The policyholder may be an association, a trustee, or any other person. Any such policy may provide, among other things, that the benefits payable thereunder are subject to reduction if the individual insured has any other coverage providing hospital, surgical or medical benefits whether on an indemnity basis or a provision of service basis resulting in such insured being eligible for more than one hundred percent of covered expenses which he or she is required to pay, and any insurer issuing individual policies providing extended hospital, surgical or medical benefits to persons sixty-five years of age and older and their spouses may also use such a policy provision. A master group policy issued to an association or to a trustee or any person appointed by an association for the purpose of providing the insurances described in this section shall be another form of group disability insurance.
Any form of policy approved by the commissioner for an association shall be offered throughout Washington to all persons sixty-five and older and their spouses, and the coverage of any person insured under such a form of policy shall not be cancellable except for nonpayment of premiums unless the coverage of all persons insured under such form of policy is also canceled.
RCW 48.21A.030