How Preliminary Injunctions Are Decided — After the CASA Ruling

A preliminary injunction is a court order freezing a government policy — or a corporate action — while a lawsuit proceeds, issued before any final ruling on the merits. It is the most consequential procedural device in public-law litigation: the orders that paused travel bans, census questions, and agency rules were all preliminary injunctions, and the Supreme Court in June 2025 reshaped their national use in CASA Inc. v. Department of Education, holding that universal injunctions — orders protecting non-parties — exceed the equitable power Congress granted the federal courts.

What is the four-factor test?

A plaintiff seeking a preliminary injunction must show, traditionally, four things: likelihood of success on the merits of the underlying claim; irreparable harm that money cannot compensate; that the balance of equities tips in the plaintiff's favor; and that an injunction serves the public interest. The test traces to the Supreme Court's 2008 Winter v. NRDC formulation. Two features carry the load in practice. Irreparable harm is the threshold: business losses usually count as compensable, so plaintiffs emphasize constitutional injuries, First Amendment chilling, or harms that will be complete before trial. Likelihood of success forces a merits preview — judges must read the statutory or constitutional claim closely enough to gauge odds, which is why injunction rulings often telegraph final outcomes.

What changed with CASA?

Before 2025, a single district judge could enjoin a policy nationwide, and both parties alternately benefited and complained: Trump-era judges froze Biden policies; Biden-era judges froze Trump policies — by early 2025, dozens of universal injunctions against one administration's actions in its first hundred days. In CASA, the Court — over dissent by Justice Ketanji Brown Jackson joined in part by the other liberals — held that such universal relief exceeds the Judiciary Act's grant of equity jurisdiction: relief runs to the parties before the court, with class certification the proper route to protect a group. The practical consequences: plaintiffs must seek class-wide injunctions under Rule 23 — a higher procedural bar requiring commonality and adequacy — or forum-shop in parallel; policies now proceed against non-parties while the named plaintiffs are protected; and states can still sue as plaintiffs with their own sovereign interests, keeping multistate coalitions as the main vehicle for broad challenges.

• Four factors: likelihood of success, irreparable harm, equities, public interest.
• CASA: no universal relief absent class certification.
• Practical shift: parallel litigation and multistate suits instead of single nationwide orders.

What are the other kinds of early relief?

A temporary restraining order is the emergency version — issued ex parte, lasting 14 days, convertible into a preliminary injunction after the other side is heard. A stay pauses the effect of a lower court's own order pending appeal, the mechanism behind the emergency or “shadow docket” applications the Supreme Court now receives weekly. Each has its own standard: stays weigh the same factors through the appellate lens, which is why the Court's emergency-docket practice — largely unsigned, unexplained orders — has drawn criticism across the ideological spectrum.

Why does this matter beyond lawyers?

Because preliminary injunctions decide what the law is, in practice, for the years a case takes: an agency rule enjoined on day one may never take effect even if ultimately upheld; a policy that survives the injunction stage often becomes fait accompli. After CASA, the question “who can stop a policy, where, and for whom” is answered narrower — and the fight has moved to class certification motions, one case at a time.

LMH News publishes information, not legal advice. Procedure follows Winter and CASA as of July 2026.