Guest Post: Mila Sohoni on Trump v. CASA

Professor Mila Sohoni of Stanford Law School, one of the nation's leading contributors to the debate over universal injunctions, weighs in on the implications of Thursday's oral argument.

I am glad to have been invited to publish this post at Divided Argument about the oral arguments yesterday in the Birthright Citizenship case. [The thoughts below were drafted rapidly this afternoon (Friday, May 16, 2025), and they do not always include direct quotation marks when I have re-used some of my own words or phrases from my earlier writings on this subject. You can find my articles here.] What follows are my reflections on two aspects of the oral argument—the discussion of the history of universal injunctions and the discussion of the Rule 23(b)(2) suit and injunctive relief for putative classes.

I. The History of the Universal Injunction and the Evolution of Equity

It was unsurprising, though somewhat dismaying, to observe that the Solicitor General Sauer offered a portrayal of the history of the universal injunction that basically echoed back Justice Thomas’s depiction of that history in Trump v. Hawaii. On Solicitor General Sauer’s portrayal, the nationwide injunction was essentially nonexistent until the 1960s when, all of a sudden, “really the first universal injunction,” Transcript at 37, popped out of the ether in Wirtz v. Baldor Electric in 1963.

But the correct origin point for thinking about injunctive relief against federal officers — and state officers — is not 1963. Nor is it 1789. Instead, the right place to look is at the early twentieth century, for that is the period in which the Court established that plaintiffs could use the injunction as a tool to block federal and state officers from bringing suit to enforce an unconstitutional law. This development — which is most famously associated with the landmark case Ex parte Young — was an innovation. Officer suits to remedy traditional common lawtorts — for example, suits for writs of trespass or ejectment — have a history that dates back to the Founding. But the filing of a lawsuit by an officer to enforce a law is not a tort of a traditional kind. “[T]he significance of Young . . . lies in its treatment of a threatened suit by an official to enforce an unconstitutional state law as if it were a common-law tort.” Idaho v. Coeur d’Alene Tribe, 521 U.S. 261, 273 (1997) (Kennedy, J., joined by Rehnquist, J., concurring) (emphasis added). This point was made in dissent in Young itself by Justice Harlan, who protested that there was a “wide difference” between officer suits to enjoin the commission of “a wrong or a trespass,” on the one hand, and the quite dissimilar type of injunction endorsed by the Young majority, viz., “a suit against officers of a State merely to test the constitutionality of a state statute, in the enforcement of which those officers will act only by formal judicial proceedings in the courts of the state.” The most recent edition of Hart & Wechsler likewise observes that “[o]ne can hardly overstate the importance of Ex parte Young’s decision to authorize injunctive relief from unconstitutional state official action” and underscores Young’s departure from “a nineteenth-century model in which constitutional issues arose incidentally (if predictably) in litigation to enforce private duties imposed by general or common law.” H&W at 1190.

The reason this matters is that essentially everyone — including this Solicitor General — accepts the legitimacy of a Young-type purely plaintiff-protective injunction against a law’s enforcement. This is true notwithstanding the fact that no such injunction against the King could have been issued by the Chancellor in England and notwithstanding the fact that 1908 came about 120 years after 1789. If we accept as legitimate equity’s evolution to allow a purely plaintiff-protective Young-type injunction (which, again, essentially everyone does accept), then one has accepted that federal courts’ power in equity can evolve beyond what chancellors did in England in 1789 and beyond what early American courts did in 1789. And once we’re at that point, then “what sense is there in drawing a line based on adherence to original meaning” between the purely plaintiff-protective injunction against enforcement and the injunction that protects not just the plaintiff but others who are vulnerable as well? See Sohoni, Lost History, at 1002-1006.

What matters, then, is not 1789, but the early twentieth century period in which Young was decided. And within a handful of years following Young, a number of injunctions issued against both federal and state officers that blocked them from enforcing laws not just against the plaintiffs, but also against those similarly situated to the plaintiffs, and sometimes against anyone at all. The Supreme Court itself issued a universal injunction in 1913 to preserve the status quo until it could resolve the constitutionality of a new federal statute imposing unpleasant new burdens on newspapers. From at least 1916 onwards, the lower federal courts also issued broad injunctions against federal and state officers that extended beyond just the plaintiffs. One of them — Pierce v. Society of Sisters — granted an injunction that categorically restrained the state from enforcing its new law against anyone; the Pierce Court expressly noted that the “prayer is for an appropriate injunction” and affirmed. See Sohoni, Amica Curiae Brief, at 2-18 (recapping the history); Sohoni, Lost History, 943-81; 989-91 (providing a much, much longer survey).

These injunctions blocked federal and state laws — and for purposes of the Article III traditions-of-equity argument and the Article III standing argument, there is no difference whatsoever between injunctions as to federal laws and injunctions as to state laws. But it is also worth noting that well before 1963 the injunction was also brought to bear against federal agency action. Precursor statutes to the Administrative Procedure Act (APA) — e.g., the Urgent Deficiencies Act — authorized federal courts to issue injunctions to restrain and set aside agency orders. In this period, agencies sometimes used orders to promulgate broad-gauged rules—for example, industry-wide regulations concerning steam engines or railroad car-hiring fees—and then, as now, lawsuits ensued to challenge those rules. In the 1920s, the 1930s, and thereafter, federal courts issued sweeping orders that enjoined these directives wholesale and vacated them. When Congress enacted the APA, the federal courts’ authority to universally vacate regulations and to enjoin them pending judicial review was then codified as a general fixture of judicial review of agency action, including rules. See 5 U.S.C. 705 and 706; Sohoni, Power to Vacate; Sohoni, Past and Future of Universal Vacatur. Congress has since “multiplied the contexts in which broad-scale agency rules may be challenged nationwide,” in statutes such as the Hobbs Act. See Sohoni, Power to Vacate, at 1176. And when Congress has wanted to restrict courts’ powers to issue broad injunctions, it has done so specifically. See 8 U.S.C. § 1252(f)(1).

Thus, when looking back at the development of the universal injunction, the key period that matters is the early twentieth century, for that is when the injunction against a law’s enforcement (both plaintiff-protective and otherwise) came to become a crucial part of “the framework of judicial safeguards that undergirds modern public law.” Sohoni, Lost History, at 1006. And certainly, the modern period is remarkable, too — mainly because an unprecedented wave of recent executive branch actions has prompted a correspondingly unprecedented wave of lawsuits and universal injunctions. But, contrary to Solicitor General Sauer’s arguments, in charting the history of the universal injunction, nothing of particular importance happened in 1963. True, the D.C. Circuit in Wirtz v. Baldor Electric ordered that an agency action should be enjoined as to the “entire industry.” But, as Professor Bray has written, Wirtz was a “pebble that sunk without causing any ripples; no subsequent cases noted the scope of the remedy in Wirtz.” Bray, Multiple Chancellors, at 439. There’s a good reason for that; Wirtz was simply another instance of a federal court exercising its equitable power to ensure that the remedy for illegal governmental conduct was both complete and practically sensible. In Wirtz, and in many cases both before and after it, that has meant an injunction that reached beyond the plaintiffs.

II. The Relief Available to a Putative Rule 23(b)(2) Class

The breakout star of the oral argument was the Rule 23(b)(2) injunctive class action—and in particular the proposition that rather than issuing universal injunctions, district courts should instead be giving preliminary injunctions to putative Rule 23(b)(2) injunctive classes. Justice Kavanaugh stated, “it seems to me … [Rule] 23(b)(2) provides a mechanism to do what’s — what’s needed here in terms of getting relief to people, and if you have PIs available for putative classes, that seems to solve — solve the issue for preliminary relief and the timing issue as well.” Transcript at 131. To unpack the point a little: the universal injunction might not be needed given that a district court has the power to speedily protect a putative class with a preliminary injunction, and this mechanism may be (in Justice Kavanaugh’s words) “the right rule … as to how things transpire in the district courts.” Transcript at 138.

But to those who are skeptical that nationwide injunctions accord with the traditions of equity, is there likewise an Article III traditions-of-equity problem with a preliminary injunction that shields a putative nationwide class? To me, of course, it makes eminent sense that federal courts should be able to give injunctive relief that shields the members of a putative class, nationwide or otherwise. The class action certification mechanism was only adopted into Rule 23 in 1966. Yet for decades before then, courts granted broad-gauged injunctive relief in representative suits under the older Federal Equity Rules and under the original 1938 version of Rule 23. In these older cases, “plaintiffs did not have to do anything more than allege in their bills of complaint that they were suing on behalf of many other persons, on a question of common interest to all of them, in order to obtain preliminary injunctions shielding all those absent parties from the law’s enforcement.” Sohoni, Lost History, at 975. In this era, courts issued injunctive relief that shielded non-parties without imposing the price tag of preclusion upon them; that relief was not objected to as running afoul of the equitable or standing limitations on federal courts’ Article III power. And the 1966 amendments to Rule 23 — which introduced the class certification mechanism — obviously did not (and could not) displace the federal courts’ existing powers in equity and Article III to give broad relief to those similarly situated to the plaintiff. On this view of affairs, there’s nothing even new, let alone illegitimate, about a court giving injunctive relief that shields members of a putative class.

At least until recently, though, many critics of the universal injunction have not seen things in this way. Instead, the critics have objected to broad-gauged injunctions in noncertified class suits just as vigorously as they have objected to decrees in suits not filed on behalf of a class. This is because they have treated the event of class certification as the crucial moment at which the court obtains the power to afford relief to absentees, because that moment is when the absentees become parties. That position, even though I disagree with it, is at least internally coherent — it “logically flows from the critics’ stance that injunctions may protect only ‘the plaintiff’; until the performative utterance of class certification, only the named plaintiff is ‘the plaintiff.’” Sohoni, Lost History, at 976 n.364. That objection also logically follows from the critics’ objection that universal injunctions unfairly create asymmetric preclusion against the federal government; the certified Rule 23(b)(2) class is binding on absentees and so does not cause the asymmetric preclusion problem. Class certification is also central to the contention that the Rule 23(b)(2) injunctive class action is the modern-day incarnation of the English bill of peace, and hence legitimate; as Solicitor General Sauer put it, the bill of peace has its sole modern-day “analogue” in the Rule 23(b)(2) class action because that type of a suit, unlike a universal injunction, “would be binding on absent class members.” Transcript at 6. For that preclusive effect to exist, though, there has to be a certified class — not just a single plaintiff saying they represent a class.

Because of all of that, and in diverse contexts, many critics of nationwide injunctions have stated that a court may not give injunctive relief to absent parties unless a case is certified as a Rule 23(b)(2) class action—either by saying as much or by emphasizing the importance of class-wide preclusion, which can only occur if a class is certified.

To sample a few instances: In IRAP, Justice Thomas objected to preliminary injunctive relief that reached beyond the plaintiff in part because “[n]o class ha[d] been certified.” IRAP, 137 S. Ct. at 2090 (Thomas, J., concurring in part and dissenting in part). Much more recently, Justices Alito and Thomas objected to the Court’s AARP I order in part because “[a]lthough the Court provided class-wide relief, the District Court never certified a class...”. They repeated their doubts about giving relief to a putative class in their dissent to today’s order (AARP II), which was issued as I was typing this post. Similarly, the DOJ has urged that preliminary injunctions be limited in scope in cases styled as class action where no class had yet been certified. See, e.g., Brief for Appellants at 57, Ramos v. Nielsen, No. 18-16981 (9th Cir. Nov. 29, 2018), 2018 WL 6420267, at *57. Indeed, the case made (in)famous as the “first” nationwide injunction, Wirtz v. Baldor Electric, was styled as a nationwide class—it was a suit brought by the plaintiffs “on behalf of themselves and all other United States manufacturers of electric motors and generators similarly situated,” id. at 533. But even though Wirtz was a representative suit, it was nonetheless denounced as an improper “national injunction” by those who oppose injunctions that give relief to non-parties.

Again, it makes sense that critics of nationwide injunctions would regard certification of the injunctive class as critical. A preliminary injunction that shields a putative injunctive class is essentially just the same thing as a universal preliminary injunction—both types of order constrain the defendant’s conduct with respect to non-parties even when that relief is not indivisible and even when that relief is not necessary to secure complete relief for the named plaintiff. Neither type of order creates preclusive effects on non-parties. And both types of order have thus been treated as equally suspect by those who contend that Article III courts may never extend protection to non-parties.

Justice Gorsuch, however, floated a different argument on Thursday that sought to put daylight between a trueuniversal injunction and a preliminary injunction to a putative class. Justice Gorsuch stated, “by proceeding through the class mechanism, even a putative class mechanism, a court is making a preliminary assessment about who are the parties [who are] going to be before it and issuing interim relief so that it preserves its jurisdiction to issue final relief with respect to those parties. And that’s very different, the argument would go, than simply saying everybody everywhere nationwide, universally … stands to benefit from this decision without ever having to suffer being bound by it.” Transcript at 132-33. Continuing the point, he posited that “there is something fundamentally different about a preliminary injunction to a putative class that you’ve found is likely to be certified and likely to succeed on the merits in order to preserve that court's jurisdiction to award ultimate relief to those parties before it … that’s categorically different than a universal injunction.” Transcript at 134.

But this doesn’t really make sense. There’s no “categorical[] differen[ce]” between these two kinds of injunctions. A plaintiff may allege in a complaint that he is suing on behalf of “everybody everywhere nationwide, universally,” but that allegation alone doesn’t make those absentees into parties. There’s another word for people who are “going to be before” the court, but who aren’t there already: we call them “non-parties.” All through these many years of debate on universal injunctions, the critics of such injunctions have resolutely insisted that injunctions may go no further than necessary to remedy the wrong done to the litigant before the court, full stop. If that line between parties and non-parties is as sacrosanct as they have insisted, then a court can’t cross that line merely because someday some non-parties alleged to be members of the class may actually be brought before the court by issuance of class certification.

Justifying such a decree on the grounds that it is necessary to preserve the court’s jurisdiction to give relief to parties who are “going to be before it” would open up a can of worms for critics of universal injunctions. For one thing, it makes it clear that court can issue an injunction that protects non-parties even if those non-parties won’t suffer any preclusive effect if the suit fails—thus abandoning the proposition (which is key to the bill of peace analogy) that to be benefitted by an injunction, one must bear the risk of preclusion. For another thing, where does that “look down the road” power run out? Consider that an individual plaintiff suing for herself alone may freely amend her complaint to add the allegation that she is proceeding as a representative of a nationwide class. If it is legitimate for a court to look down the road and give preliminary injunctive relief to preserve its jurisdiction to give relief to non-parties who may come in later via class certification, then anylawsuit — even one brought by a plaintiff suing for herself alone — that plausibly could be amended to add nationwide class claims also ought to qualify as an opportunity for the court to issue preliminary nationwide relief — for then, too, the court would only be preserving its jurisdiction over non-parties who may, in the fullness of time, ultimately become part of the case and come within the court’s jurisdiction.

Rather than unprofitably strive to put daylight between the preliminary injunction to the putative class and the universal injunction, I would instead urge that we attend to the common thread between them. When we acknowledge that a federal court can give relief to a putative class consistently with the traditions of equity (see, e.g., not just today’s AARP II order but earlier examples), even though that relief will shield non-parties who aren’t yet before the court, then we implicitly recognize a principle that transcends the class action context. A court has the Article III authority to issue a preliminary injunction that protects the members of a putative class for the same reasons that it has the authority to give a preliminary injunction that protects non-parties, full stop: the court has jurisdiction over the defendant; it has subject matter jurisdiction over the case; and it has the authority in equity to craft a decree that is both complete and sensible in the circumstances of the case at hand. Sometimes, as in AARP I and AARP II, that will mean extending relief to a putative class. Sometimes, as in IRAP, that will mean maintaining relief as to those “similarly situated to” the plaintiffs. And sometimes, as in the Birthright Citizenship case, that will mean giving relief to anyone vulnerable to the enforcement of a blatantly unconstitutional law or an order, even if no class is alleged—regardless of whether those vulnerable entities are states, associations and their members, or individuals. Rather than seeking to craft rigid categorical distinctions between such remedies, we should instead appreciate their shared conceptual foundations and recognize how each is ultimately grounded in the bedrock principle that federal courts must be equipped to supply effective and flexible remedies to shield constitutional rights.

There’s much more to say about the oral argument, but this is all that I was able to write this afternoon. I hope to be able to continue the conversation on Divided Argument in the future.