Wash. Rev. Code § 41.04.245
Any official of any local political subdivision of the state, municipal corporation, or quasi-municipal corporation authorized to disburse funds in payment of salaries and wages of employees is authorized upon written request of any employee, to deduct all or part of such employee's salary or wages for payment to any bank, savings bank, credit union, or savings and loan association if (1) the bank, savings bank, credit union, or savings and loan association is authorized to do business in this state; and (2) twenty-five or more employees of a single local political subdivision, or fewer, if a lesser number is established by such local political subdivision, authorize such a deduction for payment to the same bank, savings bank, credit union, or savings and loan association.
RCW 41.04.245