A health carrier may not pay a chiropractor less for a service or procedure identified under a particular physical medicine and rehabilitation code, evaluation and management code, or spinal manipulation code, as listed in a nationally recognized services and procedures code book such as the American medical association current procedural terminology code book, than it pays any other type of provider licensed under Title 18 RCW for a service or procedure under the same or substantially similar code, except as provided in (b) of this subsection.