Wash. Rev. Code § 15.100.140
A due and payable assessment levied in the amount determined by the commission under RCW 15.100.110 constitutes a personal debt of every person so assessed, or who otherwise owes the assessment, and the assessment is due and payable to the commission when payment is called for by the commission. If a person fails to pay the commission the full amount of the assessment by the date due, the commission may add to the unpaid assessment an amount not exceeding ten percent of the assessment to defray the cost of enforcing its collection. If the person fails to pay any due and payable assessment or other such sum, the commission may bring a civil action for collection against the person or persons in a court of competent jurisdiction. The action shall be tried and judgment rendered as in any other cause of action for a debt due and payable.
RCW 15.100.140