42 CFR § 422.574 - Parties to the organization determination.
The parties to the organization determination are -
(a) The enrollee (including his or her representative);
(b) An assignee of the enrollee (that is, a physician or other provider who has furnished a service to the enrollee and formally agrees to waive any right to payment from the enrollee for that service);
(d) Any other provider or entity (other than the MA organization) determined to have an appealable interest in the proceeding.