delivered the Opinion of the Court.
¶1 This is an appeal from the District Court’s Order and Memorandum filed January 13,1998, in the Thirteenth Judicial District Court, Big Horn County, granting summary judgment to Respondents (hereinafter collectively referred to as Thompsons); denying summary judgment to Appellants (hereinafter collectively referred to as the Tribe); and voiding three Tribal tax liens. Also raised on appeal is the trial court’s denial of the Tribe’s motion to dismiss based on, among other grounds, the Tribe’s sovereign immunity from suit. We reverse and remand for entry of an order of dismissal consistent with this opinion.
Background
¶2 Thompsons brought this action against the Tribe in state district court seeking to cancel resort tax liens imposed by the Tribe on the gross receipts of Thompsons’ business, Custer Battlefield Trading Company. While Thompsons are not members of the Crow Tribe, their business is located and conducted within the exterior boundaries of the Crow Indian Reservation and within Big Horn County. The resort tax was adopted by the Crow Tribal Council, was approved by the Area Director of the Bureau of Indian Affairs and is imposed on the consumers of the goods and services provided by Thompsons’ business. The Crow Tribal Taxation Code (CTTC) authorizes and directs the various Tribal officials to administer and enforce collection of the tax. Thompsons are required under the CTTC to collect the tax on behalf of the Tribe and to remit tax payments to the Tribe along with reporting forms.
¶3 Asa result of Thompsons’ alleged failure to comply with these requirements, the Tribe, under other provisions of the CTTC, filed with the Big Horn County Clerk and Recorder three liens against Thompsons’ business property for in excess of $200,000 in taxes claimed by the Tribe. The three liens, filed April 25, 1996, July 25, *361 1996, and September 23, 1997, are the subject of litigation in Crow Tribal Court.
¶4 Thompsons filed their action underlying this appeal in state district court on September 12,1996, seeking to void and to cancel of record the tax liens. An initial motion to dismiss based on lack of subject matter jurisdiction and sovereign immunity filed by the Tribe was denied by the trial court. Thereafter, the Tribe answered and, ultimately, the court disposed of the case and voided the Tribe’s tax liens on cross motions for summary judgment. This appeal followed.
Issues
¶5 The Tribe raises three issues on appeal.
¶6 1. Whether the Tribe and its officials have waived immunity from being sued by Thompsons in state district court?
¶7 2. Whether the state district court possessed subject matter jurisdiction over Thompsons’ cause of action?
¶8 3. Whether the Tribe’s tax liens may be voided and canceled under the provisions of § 27-1-433, MCA?
¶9 We will address Issue 1. Because this issue is dispositive, we will not address Issues 2 or 3.
Standard of Review
¶10 Where there are no genuine issues of material fact in dispute, we simply review,
de novo,
the district court’s grant and denial of the parties’ cross motions for summary judgment to determine whether the court’s decision was correct as a matter of law. Rule 56(c), M.R.Civ.P.;
Seypar, Inc. v. Water and Sewer Dist. No. 363,
Discussion
¶ 11 Before proceeding with our discussion of the merits of the sovereign immunity issue, we must first address Thompsons’ argument that the Tribe did not properly preserve this issue for appeal. Thompsons contend that this Court has no jurisdiction to decide this cause because the Tribe appealed only the trial court’s denial of its cross motion for summary judgment (which did not address sovereign immunity) and did not appeal the court’s prior denial of its motion to *362 dismiss (which was premised on, among other things, the Tribe’s immunity from suit). We conclude that Thompsons’ argument is without merit.
¶12 Sovereign immunity is in the nature of a jurisdictional defense which may be considered by a court on its own motion or at the behest of a party. It is well-settled that defenses that go to a court’s jurisdiction may be raised at any time by the parties or by the court,
sua sponte. Westlands Water Dist. v. Firebaugh Canal
(9th Cir. 1993),
¶13 Despite that the Tribe’s notice of appeal did not refer to the District Court’s denial of its motion to dismiss, the sovereign immunity issue was not only raised in the trial court and determined there, but this issue has also been raised and briefed on appeal. Accordingly, this question having been raised and being purely one of law, it is not only proper, but necessary, that we address and resolve it.
¶ 14 Turning, then, to the merits of this issue, the District Court rejected the Tribe’s claim of sovereign immunity on the basis that the Tribe’s conduct was either “outside the scope of the Tribe’s sovereignty” or “beyond their authority.” Specifically, the court ruled that in filing its liens directly in the office of the county clerk and recorder, the Tribe engaged in conduct not authorized by Montana law. The case law, however, dictates our holding that the trial court erred in its rejection of the Tribe’s sovereign immunity defense.
¶15 In
Anderson v. Engelke,
¶16 In
Kiowa Tribe of Oklahoma v. Manufacturing Technologies, Inc.
(1998), _ U.S. _,
¶ 17 In reversing Oklahoma’s courts, the Supreme Court reaffirmed its prior decisions holding that, as a matter of federal law, an Indian tribe is subject to suit only where Congress has authorized the suit or where the tribe has waived sovereign immunity. In so ruling, the Court specifically rejected the respondent corporation’s request that tribal immunity from suit be confined to transactions on the reservation and to tribal governmental activities.
Kiowa Tribe,
¶18 Specifically, the Court noted that its prior cases which sustained tribal immunity from suit had neither drawn distinctions based upon where the tribal activities occurred nor based upon distinctions between governmental activity versus commercial activity. While acknowledging that state substantive law may regulate tribal activities outside the reservation, the Court, nonetheless, noted that this “is not to say that a tribe no longer enjoys immunity from suit... [tjhere is a difference between the right to demand compliance with state laws and the means available to enforce them.’’ Kiowa
Tribe,
¶19 Moreover, the Supreme Court observed that since Indian tribes were not participants in the Constitutional Convention and were “thus not parties to the ‘mutuality of... concession’ that ’makes the State's’ surrender of immunity from suit by sister States plausible!,]’ ” tribal sovereign immunity from suit is not coextensive with state sov
*364
ereign immunity and is not subject to diminution by the states.
Kiowa Tribe,
¶20 We conclude that
Kiowa Tribe,
and the precedent cited therein, controls the disposition of the sovereign immunity issue in the case at bar. First, we are not cited to any federal authority whereby Congress has extinguished tribal sovereign immunity from suit on the basis that the Tribe filed tribal tax liens off-reservation with a county recording officer. Second, there is nothing in the record of this case that would lead us to the conclusion that the Tribe waived its defense of sovereign immunity by engaging in this conduct. In point of fact, while an Indian tribe may waive sovereign immunity, an expression of waiver must be unequivocal; waiver will not be implied.
Santa Clara Pueblo v. Martinez
(1978),
¶21 In reaching this conclusion, and in relying on
Kiowa Tribe
as the United States Supreme Court’s most recent decision on the doctrine of tribal sovereign immunity, it nevertheless bears noting that our own jurisprudence is in accord. In
Wippert,
we held that sovereign immunity barred a declaratory judgment action in state court against the Blackfeet Tribe by ranchers who borrowed money from this tribe.
Wippert,
¶22 Nonetheless, Thompsons also argue that even if the Tribe is immune from suit, the Tribal officials named as defendants in their cause of action are not. Thompsons cite
Puyallup Tribe v. Washington Game Dep’t
(1977),
¶23 As to
Imperial Granite,
the court did agree that tribal officials may lose their entitlement to the immunity of the sovereign when acting beyond their authority.
Imperial Granite,
¶24 Here (and without deciding that the Tribal officials were or were not committing a mistake of fact or law or that they were or were not acting in error) there is nothing in the record that leads to a conclusion that the Tribal officials were acting outside their official capacities or that they were acting beyond the scope of their official duties and in excess of their powers under the CTTC. Again, in the context of tribal sovereign immunity, the issue is not whether Montana law permits or prohibits the filing of tribal tax liens directly with the county recording official, but rather whether the Tribe’s officials were acting within the scope of their representational or delegated authority as agents of the Tribe in filing the Tribe’s tax liens in accordance with Tribal law. Since they were acting in that capacity in this case, the Tribe’s sovereign immunity insulates the Tribal officials from suit in state court to the same extent that the Tribe itself is immune.
¶25 Finally, without citation of authority, Thompsons suggest that since they were not seeking monetary damages in their suit against the Tribe, but were simply requesting cancellation of the Tribe’s tax liens, sovereign immunity should not apply. We are unaware of any legal basis for this argument. Indeed, Kiowa Tribe, would appear to reject any such distinction in the same manner that the Supreme Court rejected distinctions based on off-reservation versus on-reservation conduct and based on governmental versus commercial activity. Moreover, in Wippert, we applied the doctrine of sovereign immunity in a case in which there was no money damage claim against the Blackfeet Tribe. Accordingly, we reject this argument, as well.
¶26 In summary, the doctrine of tribal sovereign immunity from suit bars Thompsons’ state court action against the Tribe and against the Tribal officials in this case. The District Court was without jurisdiction to entertain Thompsons’ cause of action or to rule on the merits of their claims. The court should have taken no action other than to dismiss Thompsons’ complaint and first amended complaint.
Wippert,
¶27 Reversed and remanded for entry of an order of dismissal consistent with this opinion.
