Opinion by Judge SCHROEDER; Dissent by Judge PREGERSON.

The Public Service Company of Colorado (“PSC”) sued the Shoshone-Bannock Tribes and certain individual tribal officers, alleging that the Tribes’ attempts to regulate PSC’s shipments of spent nuclear fuel across the Shoshone-Bannock reservation were preempted by the Hazardous Materials Transportation Act, 49 U.S.C.App. §§ 1801 et seq. (West 1976 & Supp.1994) (“HMTA”). The district court held that the suit was barred by the Tribes’ sovereign immunity and PSC appeals. We reverse on the merits of the sovereign immunity claim, after first considering the Tribes’ contention that the controversy is moot.

I. Background

In the 1980s, PSC shipped spent nuclear fuel from its Fort St. Vrain Nuclear Power Plant in Plattville, Colorado to the Department of Energy’s Idaho Chemical Processing Plant pursuant to the terms of a contract between PSC and the Department of Energy. En route, these shipments crossed over *1205 the Fort Hall Indian Reservation, owned by the Shoshone-Bannock Tribes. In October of 1991, acting pursuant to 1991 tribal resolution ENVR-91-0050, Shoshone-Bannock police halted a PSC shipment at the reservation border. PSC sued under the HMTA, seeking a preliminary injunction and declaratory and injunctive relief against further interference with its shipments. The HMTA expressly provides that persons “directly affected by any requirement of [a] State or political subdivision thereof or Indian tribe,” may seek either an administrative or a judicial determination that the requirement is preempted. 49 U.S.C.A.App. § 1811(c) (Supp.1994). 1

The district court dismissed PSC’s suit, holding that the HMTA did not abrogate the Tribes’ sovereign immunity in federal court. Therefore, the court suggested, PSC was required to bring its preemption suit either in the Shoshone-Bannock tribal court, or before the Secretary of Transportation. PSC appealed.

II. Mootness

While PSC’s appeal was pending before this court, the Tribes amended resolution ENVR-91-0050 to permit shipments of spent nuclear fuel across the reservation in some circumstances. The amended ordinance, ENVR-92-S5, allows carriers to transport spent nuclear fuel across the reservation if they first obtain a permit from the Tribes, in accordance with tribal procedures. The ordinance subjects carriers to inspection requirements, notice requirements, fines, and other obligations.

The Tribes moved to dismiss this appeal, contending that it had become moot by virtue of their legislative action. PSC counters that the action is not moot, because the Tribes are still attempting to regulate shipments of spent nuclear fuel across the reservation in a manner that does not comport with federal law. PSC contends that the new ordinance imposes burdens that are impermissible under the HMTA and are therefore preempted. According to PSC, “[t]he issue here concerns not under which tribal law [the Tribes] act, but whether their conduct is illegal under federal law.”

This court’s jurisdiction is limited to cases that present actual, ongoing controversies between litigants. Lewis v. Continental Bank Corp., 494 U.S. 472, 477 , 110 S.Ct. 1249, 1253 , 108 L.Ed.2d 400 (1990). However, a controversy does not cease to exist by mere virtue of a change in the applicable law. See Lewis, 494 U.S. at 479 , 110 S.Ct. at 1254 ; Owen v. Mulligan, 640 F.2d 1130, 1133 (9th Cir.1981). Where the threatened harm still exists, or the changes in the law do not resolve the conflict, the case remains alive and suitable for judicial determination. See Lewis, 494 U.S. at 479 , 110 S.Ct. at 1254 (in order to establish continuing stake in litigation after a change in relevant law, appellant had to prove that it wished to open an uninsured bank, as to which a controversy would continue to exist, and not only the federally insured institution originally at issue).

The Tribes have merely replaced one regulation alleged to be preempted by the HMTA with another which is alleged to be similarly preempted. PSC has shown now, as it did at the outset of this case, that it is likely to be injured by the application of allegedly invalid regulations. 2 Thus, a specific controversy — whether or not the measures *1206 that the Tribes are currently taking to regulate the transportation of hazardous materials across the reservation are preempted by federal law — continues. This is no abstract or hypothetical dispute, but a continuing, concrete disagreement between the parties. 3

To decline jurisdiction merely because the precise manner in which the Tribes are allegedly violating the HMTA has changed would permit the Tribes to avoid appellate review of their actions altogether, by periodically changing the nature of their continued regulation of the shipments of hazardous materials across their reservation. Thus, even if we were to interpret PSC’s claim narrowly as one confined to the particular ordinance in effect at the time the complaint was filed, we would nevertheless take jurisdiction of the appeal as raising an issue that if moot may be capable of repetition yet evade review. See Honig v. Doe, 484 U.S. 305 , 108 S.Ct. 592 , 98 L.Ed.2d 686 (1988); Roe v. Wade, 410 U.S. 959 , 93 S.Ct. 1409 , 35 L.Ed.2d 694 (1973); see also Coral Constr. Co. v. King County, 941 F.2d 910 , 929 (9th Cir.1991) (voluntary cessation of illegal conduct doesn’t necessarily moot ease). We should not leave the Tribes with such a powerful incentive to change their regulations in order to avoid review of the district court’s ruling that the Tribes are immune from any suit in federal court. We therefore decide whether the Tribes are immune from a suit in federal court to determine preemption under the HMTA.

III. Tribal Immunity

On the merits, we agree with PSC that the district court erred in dismissing its complaint on grounds of tribal immunity. It is undisputed that Congress may abrogate a tribe’s sovereign immunity by statute. Santa Clara Pueblo v. Martinez, 436 U.S. 49, 56-58 , 98 S.Ct. 1670, 1675-77 , 56 L.Ed.2d 106 (1978). However, courts should “ ‘tread lightly in the absence of clear indications of legislative intent’ when determining whether a particular federal statute waives tribal sovereign immunity.” Northern States Power Co. v. Prairie Island Mdewakanton Sioux Indian Community, 991 F.2d 458 , 462 (8th Cir.1993) (quoting Santa Clara, 436 U.S. at 56 , 98 S.Ct. at 1675 ). As the Supreme Court has stated, such a waiver of sovereign immunity must be unequivocally expressed. See id. at 58 , 98 S.Ct. at 1676 . We conclude, as the Eighth Circuit did in Northern States Power, that § 1811 contains such an express waiver of tribal immunity.

Section 1811 states that “[a]ny person, including a State or political subdivision thereof or Indian tribe, directly affected by any requirement of a State or political subdivision or Indian tribe, may apply to the Secretary ... for a determination of whether that requirement is preempted.” 49 U.S.C.App. § 1811(e)(1). If an administrative decision is sought pursuant to § 1811(c)(1), “a party to [that] proceeding ... may seek review by the appropriate district court of the United States.... ” § 1811(e). Alternatively, the statute discusses the possibility of filing a direct district court action:

49 U.S.CApp. § 1811(c)(2).

By its terms, § 1811 clearly contemplates that Indian tribes may be sued in court if they enact regulations that are alleged to be *1207 preempted by the HMTA. Section 1811 subjects tribal regulations to its preemption provisions, 49 U.S.C.App. § 1811(a), and provides that affected parties may seek preemption determinations regarding those regulations in “any court of competent jurisdiction.” 49 U.S.CApp. § 1811(c)(2). As the Eighth Circuit noted, similarly concluding that § 1811 abrogates immunity to permit preemption suits in district court against tribes:

Northern States Power, 991 F.2d at 462.

Section 1811 therefore necessarily abrogates the tribes’ immunity from suit, at least in some forums. The suggestion that subsection (c)(2) applies only to suits against non-immune entities is not tenable, because only tribes and states, both of which enjoy sovereign immunity from suit, are subject to the provisions of § 1811. The only question, then, is whether § 1811 abrogates tribal immunity from suit in federal court, as opposed to tribal or state court. We believe that it does.

Federal courts generally have jurisdiction over questions of federal law. 28 U.S.C. § 1331 . Thus, § 1811’s reference to “court[s] of competent jurisdiction” would logically appear to include federal courts. In addition, it is clear that Indian tribes may be haled into federal court under § 1811 pursuant to the administrative alternative to § 1811(e)(2) set forth in §§ 1811(e)(1) & (e). Subsection (e) of section 1811 specifically provides that the Secretary’s administrative preemption determination is subject to review in “the appropriate district court of the United States.” Given that tribes are not immune from suit in federal court pursuant to §§ 1811(c)(1) and (e), it would be anomalous to conclude that those same federal courts are not “competent” to decide the same issue of federal law between the same parties when § 1811(c)(l)’s alternative, § 1811(c)(2), is invoked. In short, by providing that tribal regulations may be challenged in preemption suits that may be heard in federal court, Congress effectively abrogated any tribal immunity from such suits.

Because the Tribes themselves are not protected by tribal immunity, tribal officers acting in their official capacity may also be sued under the HMTA. The district court erred in dismissing appellant’s complaint under principles of tribal immunity.

REVERSED and REMANDED.

. Section 1811(a) provides generally that state and tribal regulation of hazardous material transportation is preempted if it is inconsistent with the HMTA. Section 1811(c) then sets forth the remedies available to persons burdened by a state or tribal regulation that is arguably invalid under subsection (a). Section 1811(c)(1) provides that such persons or entities “may apply to the Secretary ... for determination of whether that requirement is preempted.... ” Alternatively, § 1811(c)(2) provides, in full:

. In so stating, we express no opinion as to the validity of the past or current regulations. For purposes of the HMTA, an affected party is entitled to seek a judicial determination of preemption if state or tribal regulations are applied to it.

. The dissent points out that PSC has temporarily ceased shipping spent nuclear fuel into Idaho, pending completion of an environmental impact statement. We agree that if the Tribe had shown that any such shipments were unlikely to resume at any time in the future, the case would be moot. However, "[i]f a party to an appeal suggests that the controversy has, since the rendering of judgment below, become moot, that party bears the burden of coming forward with the subsequent events that have produced that alleged result." Cardinal Chemical Co. v. Morton Int’l, - U.S. -, --, 113 S.Ct. 1967, 1976 , 124 L.Ed.2d 1 (1993) (citing United States v. W.T. Grant Co., 345 U.S. 629, 633 , 73 S.Ct. 894, 897 , 97 L.Ed. 1303 (1953). There is no basis in this record for concluding that the environmental impact statement currently under preparation is likely to result in a permanent ban on any shipments of spent nuclear fuel in Idaho.