Wash. Rev. Code § 50.04.220
The term "employment" shall not include service with respect to which unemployment compensation is payable under an unemployment compensation system established by an act of congress: PROVIDED, That the commissioner is hereby authorized to enter into agreements with the proper agencies under such act of congress, which agreements shall become effective ten days after publication thereof in the manner provided in this title for publication of general rules, to provide reciprocal treatment to individuals who have, after acquiring potential rights to benefits under this title, acquired right to unemployment compensation under such act of congress, or who have, after acquiring potential rights to unemployment compensation under such act of congress, acquired rights to benefits under this title.
RCW 50.04.220