Here is the complaint, filed in Central District of California: Santa Ynez v US Complaint.

An excerpt:

11. During 2003 and 2004, Santa Ynez made “per capita” payments to its members from revenues derived from gaming activities. Federal law, at 25 U.S.C. § 2710(b)(3)(D), makes such payments subject to federal income taxation and 26 U.S.C. § 3402(r) make such payments subject to federal withholding requirements.

12. During 2003 and 2004, Santa Ynez failed to withhold, or underwithheld, federal taxes on payments made to some tribal members.

13. The IRS later conducted an audit of Santa Ynez for those years and assessed taxes, interest and penalties against the Tribe for 2003 and 2004.

14. On or about May 5, 2006, Santa Ynez paid the IRS $1,041,745.11 for tax year 2003 and $2,891,865.76 for tax year 2004 in full satisfaction of all amounts ostensibly owed under the audit.

15. Upon information and belief, the IRS received and credited the Tribe’s tax payments on or about May 10, 2006.

16. Subsequent to making its May, 2006 tax payments to the IRS, the Tribe determined that all, or virtually all, of the tribal members whose taxes had not been withheld, or had been underwithheld, had reported and fully paid their federal income taxes for years 2003 and 2004. As a result, the Tribe overpaid its withholding tax obligation for years 2003 and 2004.