25 U.S. Code § 1621s - Prompt action on payment of claims
(a) Time of response
The Service shall respond to a notification of a claim by a provider of a contract care service with either an individual purchase order or a denial of the claim within 5 working days after the receipt of such notification.
(b) Failure to timely respond
If the Service fails to respond to a notification of a claim in accordance with subsection (a) of this section, the Service shall accept as valid the claim submitted by the provider of a contract care service.