42 CFR §424.73

1. (a)Basic prohibition. Except as specified in paragraph (b) of this section, Medicare does not pay amounts that are due a provider to any other person under assignment, or power of attorney, or any other direct payment arrangement.
2. (b)Exceptions to the prohibition—(1) Payment to a government agency or entity. Subject to the requirements of the Assignment of Claims Act (31 U.S.C. 3727), Medicare may pay a government agency or entity under an assignment by the provider.
   1. (2)Payment under assignment established by court order. Medicare may pay under an assignment established by, or in accordance with, the order of a court of competent jurisdiction if the assignment meets the conditions set forth in § 424.90.
   2. (3)Payment to an agent. Medicare may pay an agent who furnishes billing and collection services to the provider if the following conditions are met:
      1. (i)The agent receives the payment under an agency agreement with the provider;
      2. (ii)The agent's compensation is not related in any way to the dollar amounts billed or collected;
      3. (iii)The agent's compensation is not dependent upon the actual collection of payment;
      4. (iv)The agent acts under payment disposition instructions that the provider may modify or revoke at any time; and
      5. (v)The agent, in receiving the payment, acts only on behalf of the provider.