ZIMMER, J.

The Sac and Fox Tribe of the Mississippi in Iowa (Tribe) appeals from the juvenile court's denial of its motion to intervene in two termination of parental rights cases that involve children the Tribe alleges are Indian children within the context of the federal Indian Child Welfare Act (ICWA). We affirm the juvenile court.

I. Background Facts and Proceedings.

Kadance, born February 1, 2001, and Kristopher, born January 26, 2002, are the children of Kristie, a Tribe member. Neither child is a Tribe member, and neither Kadance's father Dale, nor Kristopher's father, Christopher, is a Native American.

The State initiated child in need of assistance (CINA) proceedings, first in regard to Kadance, then in regard to Kristopher. The Tribe received proper notice of each CINA proceeding. In each case the Tribe took the position, through Sandra Morrison, an ICWA Social Worker employed by the Tribe's family services organization, that the child was neither an enrolled member of the Tribe nor eligible for enrollment, and thus not an Indian child for the purposes of ICWA. The juvenile court adjudicated both Kadance and Kristopher as children in need of assistance. In Kadance's case, the court made specific findings that ICWA was not applicable. Neither CINA adjudication was appealed.

In December 2001 the State filed a petition to terminate Kristie and Dale's parental rights to Kadance. When the matter came on for hearing in February 2002, Kristie and Dale stipulated to the allegations in the petition. During the hearing Sandra Morrison once again confirmed that Kadance was not eligible for enrollment in the Tribe. In its order terminating Kristie and Dale's parental rights, the juvenile court stated that "all parties are in agreement that the Indian Child Welfare Act is not applicable to Kandance. . . ." The termination order was not appealed.

In December 2002 the State filed a petition to terminate Kristie and Christopher's parental rights to Kristopher. The petition was still pending when, in February 2003, the Tribe filed a motion to intervene in both termination cases. In its motion, the Tribe reversed its position regarding each of the children. The Tribe now claimed the children were eligible for enrollment, based on one of the two membership provisions in its constitution, as well as a 1997 resolution that defined eligibility for the purposes of ICWA.

In a March 2003 order the juvenile court denied the Tribe's motion to intervene. The court determined that, despite the resolution, under the plain language of the Tribe's constitution and by-laws the children were not eligible for enrollment. The following day the court terminated Kristie and Christopher's parental rights to Kristopher. The Tribe filed an interlocutory appeal, which was granted by the supreme court.

II. Scope of Review.

We review the denial of a motion to intervene for the correction of errors at law. In re H.N.B., 619 N.W.2d 340, 342 (Iowa 2000).

III. Discussion.

ICWA is applicable in a State court proceeding to terminate parental rights if the child involved in the proceeding is an "Indian child." 25 U.S.C. § 1903(1)(ii), (4) (2001). ICWA defines an Indian child as a person under eighteen years of age, unmarried, and "either (a) a member of an Indian tribe or (b) is eligible for membership in an Indian tribe and is the biological child of a member of an Indian tribe. . . ." Id. § 1903(4). If the termination proceeding does involve an Indian child, then the tribe of which that child is or is eligible to become a member has a statutory "right to intervene at any point in the proceeding." 25 U.S.C. § 1903(5), 1911(c). Thus, the key question on appeal is whether the Tribe met its burden to show Kadance and Kristopher are Indian children as defined by ICWA. See in re J.D.B., 584 N.W.2d 577, 582 (Iowa Ct.App. 1998) (citations omitted) ("`[I]t is incumbent upon the party asserting applicability of ICWA to prove the child meets the criteria under ICWA.'").

A. Estoppel.

As an initial matter the State contends that, in light of the Tribe's prior assertions that Kadance and Kristopher were not eligible for membership, the doctrines of equitable estoppel, judicial estoppel and estoppel by acquiescence prevent the Tribe from now asserting the children are in fact eligible for membership. The Tribe responds, in essence, that its statutory right of intervention under ICWA preempts these state-law doctrines. However, this argument presupposes the children are in fact eligible for membership, and thus ICWA applies to the termination proceedings. See J.D.B., 584 N.W.2d at 582 ("The provisions of ICWA do not apply until the court determines the children are `Indian' as defined in ICWA."). As will be discussed in the next portion of our opinion, we conclude ICWA did not apply to the termination proceedings in this matter. While we could accordingly decline to address the State's estoppel arguments, we believe an analysis of the issue would be beneficial to the resolution of some future ICWA-related proceedings.

We have previously addressed the issue of a potential conflict between ICWA and Iowa law in an appeal from the termination of parental rights. In In re J.D.B., this court considered the question of whether Iowa's error preservation rules would apply in a proceeding governed by ICWA. Id. at 581. We concluded ICWA neither expressly nor impliedly preempted our rules of error preservation, and that "[t]o have our procedural rules preempted by federal law, would serve no greater purpose under ICWA." Id. Although we continue to hold to our analysis in that case, we conclude the circumstances presented in this matter require us to reach a different conclusion regarding the applicability of the doctrines of estoppel.

As a general proposition, state law will be preempted when it "`conflicts with the express terms of federal law' and `sufficiently injure[s] the objectives of [a] federal program[,]'" or does "`major damage' to `clear and substantial' federal interests." In re Marriage of Trickey, 589 N.W.2d 753, 756-57 (Iowa Ct.App. 1998) (citation omitted). However, when the state law is one affecting Indian tribes, courts must consider the nature of any competing state, federal and tribal interests. See New Mexico v. Mescalero Apache Tribe, 462 U.S. 324, 333-34, 103 S.Ct. 2378, 2386-87, 76 L.Ed.2d 611, 619-20 (1983). In such cases state jurisdiction over an action or issue is preempted if "it interferes or is incompatible with federal and tribal interests reflected in federal law, unless the state interests at stake are sufficient to justify the assertion of state authority." Id.

One of the primary purposes of ICWA is "to protect the best interests of Indian children and to promote stability and security of Indian tribes and families by the establishment of minimum Federal standards for the removal of Indian children from their families. . . ." 25 U.S.C. § 1902. In seeking to promote tribal interests, Congress provided tribes with two broad and largely uncircumscribed rights regarding intervention in termination of parental rights proceedings. As previously noted, an Indian child's tribe has the right to intervene "at any point" in a proceeding to terminate parental rights. Id. § 1911(c). In addition, if a tribe can show that a termination occurred in violation of the tribe's right of intervention, the tribe may petition for invalidation of the termination. Id. § 1914. Clearly, state law that would preclude a tribe from exercising its statutory right of intervention would interfere with the tribal interests evidenced by ICWA.

We must therefore balance the competing state and tribal interests. Mescalero Apache Tribe, 462 U.S. at 333-34, 103 S.Ct. at 2386-87, 76 L.Ed.2d. at 619-20. It is clear that a tribe's interest in participating in a proceeding involving the future of an Indian child is not only significant, but one which the federal government seeks to vigorously protect. See State ex rel. Juvenile Dept. of Lane County v. Shuey, 850 P.2d 378, 381 (Or.Ct.App. 1993) ("Tribal participation in state custody proceedings involving Indian children is essential to effecting the purposes of the ICWA."). The State's interest in judicial economy and avoiding duplicative proceedings pales in comparison. Accordingly, we conclude that when a tribe has a statutory right of intervention under ICWA, state-law doctrines of estoppel may not be applied to deprive it of that right. However, for the reasons which follow, we conclude that in this case the Tribe failed to establish a statutory right of intervention.

B. Eligibility for Enrollment.

Before we address the question of whether Kadance and Kristopher were "Indian children" within the meaning of ICWA, we feel the need to clarify the role of the courts in such determinations. We agree with the Tribe that it is "the arbitrator of [its] own membership." In re J.W., 498 N.W.2d 417, 422 (Iowa Ct.App. 1993). We also agree the courts should respect a Tribe's interpretation of its membership provisions. However, a Tribe's discretion to declare that a particular child meets previously-articulated eligibility criteria cannot be without limits. When a tribe formally adopts membership criteria, the courts must ultimately be guided by those criteria in determining whether the tribe has met its burden of establishing that a particular child is an Indian child within the meaning of ICWA. See In re J.D.B., 584 N.W.2d 577, 582 (Iowa Ct.App. 1998) (indicating that while it is a tribe's burden to present evidence of eligibility, ultimate determination of ICWA's applicability is matter for the court).

We therefore turn to the Tribe's membership provisions. Article II, Section 1 of the Constitution and Bylaws of the Sac and Fox Tribe of the Mississippi in Iowa defines tribal membership. The Tribe concedes none of the provisions of Section 1 apply to Kadance or Kristopher. The Tribe argues, however, that Kadance and Kristopher are eligible for membership in the Tribe pursuant to Article II, Section 2:

Sec. 2. Persons who are descendants of members of this Tribe but not entitled to membership under Section 1 may be adopted into the Sac and Fox Tribe by a majority vote of the Tribal Council, providing that such persons have resided on the reservation for a period of five years.

(a) The application for membership into the Tribe shall be made by self, parents, or guardians to the Membership Committee of the Tribal Council, and thereupon the said committee shall investigate for the Tribal Counsel to determine the desirability of adoption.

(b) Persons adopted under this section shall not be entitled to hold office under this Constitution or participate in the payments resulting from the treaties of the Tribe with the United States, but may enjoy other privileges of tribal members.

We cannot agree with the Tribe's position. By its very terms, Section 2 cannot apply to Kadance and Kristopher. Neither child has reached five years of age and therefore has not "resided on the reservation for a period of five years." The Tribe contends the court must recognize the children's potential, prospective right to membership. However, ICWA defines an Indian child as one who "is eligible" for membership, demonstrating an intent that an Indian child be presently eligible for membership. Kadance and Kristopher are not presently eligible for membership in the Tribe under Section 2.

The Tribe next relies on Sac and Fox Tribal Resolution No. 26, 1997. That document

interprets and clarifies that . . . Section 2 is not intended to apply in a manner that would preclude eligibility for membership of children of Sac and Fox descent who have not yet attained the age of 5 and whose father is not an enrolled Sac and Fox member; and . . . that, for purposes of the Indian Child Welfare Act of 1978, the Tribe hereby considers all children of Sac and Fox descent regardless of age and residence to be eligible for membership in the Tribe until such point that enrollment is denied. . . .

If this resolution was in fact adopted by the Tribe's governing council in the exercise of its authority, it must be given full force and effect by the courts. See Iowa Code § 1.14 (2001). ICWA also requires courts to give full faith and credit to a public act or record of the Tribe to the extent that the courts would accord full faith and credit to the public act or record of another entity. 21 U.S.C. § 1911(d).

Upon careful review of the rather limited record in this case, we conclude the Tribe has not established the resolution is of binding effect. See J.D.B., 584 N.W.2d at 582 (citations omitted) ("`[I]t is incumbent upon the party asserting applicability of ICWA to prove the child meets the criteria under ICWA.'"). The portion of the Tribe's Constitution and Bylaws that apparently governs resolutions, Article X, was not made a part of the record in either termination proceeding. We are therefore unable to ascertain if the resolution was in fact adopted in accordance with the Tribe's Constitution and Bylaws or under a proper exercise of the tribal council's authority. Nor are we able to determine what effect such a resolution has under tribal law.

The Tribe has failed it its burden to demonstrate that ICWA is applicable to these termination proceedings. Accordingly, it had no statutory right of intervention. We affirm the juvenile court's denial of the Tribe's motion to intervene. AFFIRMED.