42 C.F.R. § 136.24
Authorization for contract health services
(a) No payment will be made for medical care and services obtained from non-Service providers or in non-Service facilities unless the applicable requirements of paragraphs (b) and (c) of this section have been met and a purchase order for the care and services has been issued by the appropriate ordering official to the medical care provider.
(b) In nonemergency cases, a sick or disabled Indian, an individual or agency acting on behalf of the Indian, or the medical care provider shall, prior to the provision of medical care and services notify the appropriate ordering official of the need for services and supply information that the ordering official deems necessary to determine the relative medical need for the services and the individual's eligibility. The requirement for notice prior to providing medical care and services under this paragraph may be waived by the ordering official if:
(1) Such notice and information are provided within 72 hours after the beginning of treatment or admission to a health care facility; and
(2) The ordering official determines that giving of notice prior to obtaining the medical care and services was impracticable or that other good cause exists for the failure to provide prior notice.
(c) In emergency cases, a sick or disabled Indian, or an individual or agency acting on behalf of the Indian, or the medical care provider shall within 72 hours after the beginning of treatment for the condition or after admission to a health care facility notify the appropriate ordering official of the fact of the admission or treatment, together with information necessary to determine the relative medical need for the services and the eligibility of the Indian for the services. The 72-hour period may be extended if the ordering official determines that notification within the prescribed period was impracticable or that other good cause exists for the failure to comply.