Section 421.104 - Assignment of providers of services to intermediaries during transition to Medicare Administrative Contractors (MACs)(a) Beginning October 1, 2005, CMS assigns providers of services and other entities that may bill Part A benefits to intermediaries in a manner that will best support the transition to Medicare Administrative Contractors (MACs) under section 1874A of the Act in accordance with subpart E of this part.(b) These providers of services and other entities must continue to bill the intermediary that they were billing prior to October 1, 2005, until one of the following events occurs: (1) The intermediary's agreement with CMS ends, and the provider or entity is directed by CMS to bill another CMS contractor.(2) The provider or entity is assigned to a MAC that has begun to administer claims within the geographic locale of the provider or entity.(3) CMS directs the provider or entity to begin billing another CMS contractor in order to support the implementation of MACs under section 1874A of the Act and subpart E of this part.(c) New providers of services and new entities will be assigned to the intermediary serving their geographic locale if no MAC has begun to administer Medicare claims in the locale. These providers or entities must continue to bill the intermediary until one of the events in paragraph (b) of this section occurs.(d) Providers or entities will only be granted exceptions to the provisions of paragraphs (b) or (c) of this section if CMS deems the exception to be in the compelling interest of the Medicare program.(e) CMS will notify the provider or entity, the outgoing intermediary, and the newly assigned intermediary of assignment or reassignment decisions. 71 FR 68228 , Nov. 24, 2006