Wash. Rev. Code § 39.06.020
A public works contractor must verify responsibility criteria for each first tier subcontractor, and a subcontractor of any tier that hires other subcontractors must verify responsibility criteria for each of its subcontractors. Verification shall include that each subcontractor, at the time of subcontract execution, meets the responsibility criteria listed in RCW 39.04.350(1) and possesses an electrical contractor license, if required by chapter 19.28 RCW, an elevator contractor license, if required by chapter 70.87 RCW, or a plumbing contractor license[,] if required by chapter 18.106 RCW. This verification requirement, as well as the responsibility criteria, must be included in every public works contract and subcontract of every tier.
RCW 39.06.020