36 C.F.R. § 1250.70

You may appeal when there is any adverse determination, including:

(a) Refusal to release a record, either in whole or in part;

(b) Determination that a record does not exist or cannot be found;

(c) Determination that the record you sought was not subject to the FOIA;

(d) Denial of a request for expedited processing;

(e) Denial of a fee waiver request; or

(f) Fee category determination.