Here is the opinion in Miccosukee Tribe of Indians v. United States.

An excerpt:

This appeal presents three issues: (1) whether the Miccosukee Tribe may assert tribal sovereign immunity to quash summonses issued to third-party financial institutions by the Commissioner of the Internal Revenue Service to obtain tribal financial records relevant to an ongoing tax investigation; (2) whether the Commissioner issued the summonses for a proper purpose; and (3) whether the Tribe has standing to bring an overbreadth challenge to summonses issued to third parties and, if so, whether the summonses were overbroad. In 2010, the Commissioner issued four summonses to third-party financial institutions to determine whether the Tribe had complied with its federal withholding requirements during the period from 2006 to 2009. The Tribe petitioned to quash the summonses on the grounds of sovereign immunity, improper purpose, relevance, bad faith, and overbreadth. The district court denied those petitions. Because we conclude that tribal sovereign immunity does not bar the issuance of these third-party summonses, the district court did not clearly err when it found that the summonses were issued for a proper purpose, and the Tribe lacks standing to challenge the summonses for overbreadth, we affirm.

Briefs are here.

Lower court materials here.