Wash. Rev. Code § 19.68.030
The license of any person so licensed may be revoked or suspended if he or she has directly or indirectly requested, received, or participated in the division, transference, assignment, rebate, splitting, or refunding of a fee for, or has directly or indirectly requested, received, or profited by means of a credit or other valuable consideration as a commission, discount, or gratuity in connection with the furnishing of medical, surgical, or dental care, diagnosis or treatment or service, including X-ray examination and treatment, or for or in connection with the sale, rental, supplying or furnishing of clinical laboratory service or supplies, X-ray services or supplies, inhalation therapy service or equipment, ambulance service, hospital or medical supplies, physiotherapy or other therapeutic service or equipment, artificial limbs, teeth, or eyes, orthopedic or surgical appliances or supplies, optical appliances, supplies or equipment, devices for aid of hearing, drugs, medication or medical supplies or any other goods, services or supplies prescribed for medical diagnosis, care or treatment, except payment, not to exceed thirty-three and one-third percent of any fee received for X-ray examination, diagnosis, or treatment, to any hospital furnishing facilities for such examination, diagnosis, or treatment.
RCW 19.68.030