Wash. Rev. Code § 15.26.220
In the event any person fails to pay the full amount of such assessment or such other sum on or before the due date, the commission may add to such unpaid assessment or sum an amount not more than ten percent but not less than one dollar of the same to defray the cost of enforcing the collection of such assessment, together with interest on the unpaid balance of one percent per month commencing the first month following the month in which payment was due. In the event of failure of such person or persons to pay any such due and payable assessment or other such sum, the commission may bring a civil action against such person or persons in a state court of competent jurisdiction for the collection thereof, together with the interest and the above specified ten percent thereon, and such reasonable attorneys' fees as may be allowed by the court, and such action shall be tried and judgment rendered as in any other cause of action for debt due and payable.
RCW 15.26.220