Welcome to 2026! Once again, the past year was a big year at the Supreme Court. Among the decisions it handed down, Trump v. CASA, Inc. dramatically altered the kind of emergency relief plaintiffs can seek from harmful government actions. Lower courts are still figuring out how to apply the decision’s holding.
What Did the Supreme Court Decide in CASA?
CASA arose from a dispute about birthright citizenship. Executive Order No. 14,160 declared it the “policy of the United States” to no longer recognize citizenship for children born to parents who were neither citizens nor lawful permanent residents at the time of birth. Individuals, organizations, and states sued almost immediately in three separate district courts, and all three courts issued a universal preliminary injunction — that is, a temporary order preventing the E.O. from applying to anyone in the U.S. while the case proceeded towards a final decision, in order to avoid the risk of irreparable harm. The three birthright citizenship cases quickly made it to the Supreme Court. But the Supreme Court didn’t actually consider the citizenship question. Instead, the Court’s decision in CASA resolved a procedural issue: are district courts allowed to grant injunctions that apply to anyone in the U.S. (referred to as “universal injunctions”), rather than just the plaintiffs in the lawsuit?
As academic as it sounds, the answer to that question has extremely high stakes. Universal injunctions have been a powerful — and, over the last decade, widely used — tool to stop executive actions from taking effect. On the one hand, as the CASA majority opinion noted, these days almost every major presidential action is immediately frozen by a district court. See CASA, 606 U.S. at 840. That essentially prevents it from taking effect anywhere until litigation concludes (which can often take years). On the other hand, as the dissent from Justices Sotomayor, Kagan, and Jackson pointed out, when the government does something plainly illegal, it’s a problem if courts can only stop the Executive Branch from enforcing it against those who have managed to sue right off the bat. See CASA, 606 U.S. at 879–80 (Sotomayor, J., dissenting).
Ultimately, the outcome of the case came down to a historical analysis. The Court decided that, because the universal injunction did not exist in 1789 (when Congress passed the original Judiciary Act, setting out the kinds of relief courts can grant), district courts today are only allowed to issue injunctions that provide “complete relief” to the specific people who have sued.
Of course, there are caveats. Issuing “complete relief” to some plaintiffs might sometimes make a nationwide remedy necessary — in fact, two of the lower courts considering the birthright citizenship E.O. after CASA decided to issue nationwide relief again on that basis. See Doe v. Trump, Nos. 25-1169, 25-1170, 2025 WL 2814730, at *34–*35 (1st Cir. Oct. 3, 2025); Washington v. Trump, 145 F.4th 1013 (9th Cir. 2025), affirming State v. Trump, 765 F. Supp. 3d 1142 (W.D. Wash. 2025). District courts are also (still) allowed to certify nationwide class actions (a type of lawsuit where one or several plaintiffs file on behalf of a larger group of similarly situated people). And, as Justice Kavanaugh noted in his concurrence, district courts can award preliminary nationwide relief “when such relief is legally authorized,” e.g., spelled out in a statute. See CASA, 606 U.S. at 869 (Kavanaugh, J., concurring).
So, what does this mean for imperiled species?
The biggest takeaway is: many (if not most) challenges to federal government actions that harm listed species come under the Administrative Procedure Act. Justice Kavanaugh states in his concurrence that CASA doesn’t change district courts’ authority to invalidate new agency rules under section 706 of the Administrative Procedure Act. See CASA, 606 U.S. at 869 (Kavanaugh, J., concurring). But section 706 does not address preliminary relief — the section covering that is 705, which none of the Justices mentioned anywhere in majority opinion, the concurrences, or the dissents.
Section 705 authorizes courts to “issue all necessary and appropriate process to postpone the effective date of an agency action or to preserve status or rights pending conclusion of the review proceedings.” 5 U.S.C. 705. But section 705 says nothing about scope. So, does that count as “legally authorizing” a universal injunction? Courts have already started to express different opinions on this. Decisions in several circuits have indicated that CASA shouldn’t prevent universal relief issued under either section 705 or 706 of the Administrative Procedure Act, while at least one Ninth Circuit decision has found, on the facts of that case, that CASA’s “complete relief” principle provides “useful guidance” for relief issued under section 705. See Immigrant Defs. Law Ctr. v. Noem, No. 25-2581, 2025 WL 2017247, at *14 (9th Cir. July 18, 2025).
In conclusion, CASA left a lot of questions unanswered and time will tell how the lower courts apply its holding. In the meantime, conservation plaintiffs will have to carefully apply and distinguish CASA in upcoming cases.
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