Here is the opinion in State of Kansas v. Zinke.

An excerpt:

The question in this case is whether a legal opinion letter issued by the Acting General Counsel of the National Indian Gaming Commission (“NIGC”) regarding the eligibility of Indian lands for gaming constitutes “final agency action” subject to judicial review. In response to a request from the Quapaw Tribe, the NIGC Acting General Counsel issued a legal opinion letter stating that the Tribe’s Kansas trust land was eligible for gaming under the Indian Gaming Regulatory Act (“IGRA”). The State of Kansas and the Board of County Commissioners of the County of Cherokee, Kansas, filed suit, arguing that the letter was arbitrary, capricious, and erroneous as a matter of law. The district court concluded that the letter did not constitute reviewable final agency action under IGRA or the Administrative Procedure Act (“APA”).

Exercising jurisdiction under 28 U.S.C. § 1291, we affirm. IGRA’s text, statutory scheme, legislative history, and attendant regulations demonstrate congressional intent to preclude judicial review of legal opinion letters. Further, the Acting General Counsel’s letter does not constitute final agency action under the APA because it has not determined any rights or obligations or produced legal consequences. In short, the letter merely expresses an advisory, non-binding opinion, without any legal effect on the status quo ante.

Briefs here.