25 CFR §900.29

1. (a)To advise the Indian tribe or tribal organization in writing of the Secretary's objections, including a specific finding that clearly demonstrates that (or that is supported by a controlling legal authority that) one of the conditions set forth in § 900.22 exists, together with a detailed explanation of the reason for the decision to decline the proposal and, within 20 days, any documents relied on in making the decision; and
2. (b)To advise the Indian tribe or tribal organization in writing of the rights described in § 900.31.