5 C.F.R. § 1820.5 – Responses to requests.

(a) General. Ordinarily, OSC shall have 20 business days from when a request is received to determine whether to grant or deny the request. Once OSC makes a determination to grant a FOIA request for records, or makes an adverse determination denying a request in any respect, it will notify the requester in writing. Adverse determinations, or denials of requests, consist of: A determination to withhold any requested record in whole or in part; a determination that a requested record does not exist or cannot be located; a determination that a record is not readily reproducible in the form or format sought by the requester; a determination that what has been requested is not a record subject to the FOIA; a determination on any disputed fee matter, including a denial of a request for a fee waiver; and a denial of a request for expedited treatment.
(b) Adverse determinations. A notification to a requester of an adverse determination on a request shall include:
1. (1) A brief statement of the reason(s) for the denial of the request, including any FOIA exemption applied by OSC in denying the request; and
2. (2) A statement that the denial may be appealed under section 1820.6(a), with a description of the requirements of that subsection.