42 CFR §411.6

1. (a)Basic rule. Except as provided in paragraph (b) of this section, Medicare does not pay for services furnished by a Federal provider of services or other Federal agency.
2. (b)Exceptions. Payment may be made—
   1. (1)For emergency hospital services, if the conditions of § 424.103 of this chapter are met;
   2. (2)For services furnished by a participating Federal provider which CMS has determined is providing services to the public generally as a community institution or agency;
   3. (3)For services furnished by participating hospitals and SNFs of the Indian Health Service; and
   4. (4)For services furnished under arrangements (as defined in § 409.3 of this chapter) made by a participating hospital.