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Preliminary Injunction Requirements in Federal Court

A plaintiff seeking a preliminary injunction in federal court must satisfy a four-factor test and comply with Federal Rule of Civil Procedure 65's procedural requirements.

• Likelihood of success on the merits — the movant must show it is likely to succeed on the merits of its claim. Winter v. Natural Resources Defense Council, Inc., 555 U.S. 71 (well-settled — binding, U.S. Supreme Court)
• Likely irreparable harm — the movant must show it is likely to suffer irreparable harm absent preliminary relief; a mere "possibility" of harm is insufficient. (well-settled)
• Balance of equities — the court must weigh the competing claims of injury to each party. (well-settled)
• Public interest — the injunction must be in the public interest. (well-settled)
• Security/bond — the court may issue a preliminary injunction only if the movant posts security in an amount the court deems proper (the U.S. and its agencies are exempted). Court Rule 65: Injunctions and Restraining Orders2 (well-settled)

The Winter Four-Factor Test

In Winter v. Natural Resources Defense Council, Inc., 555 U.S. 7 (2009) (binding — U.S. Supreme Court), the Court articulated the controlling standard:

"A plaintiff seeking a preliminary injunction must establish that he is likely to succeed on the merits, that he is likely to suffer irreparable harm in the absence of preliminary relief, that the balance of equities tips in his favor, and that an injunction is in the public interest." A plaintiff seeking a preliminary injunction must establish that he is likely to succeed on the merits, that he is likely to suffer irreparable harm in the absence of preliminary relief, that the balance of equities tips in his favor, and that an injunction is in the public interest.

The Court was explicit that the lower courts' more lenient "possibility of irreparable harm" standard was wrong: "Our frequently reiterated standard requires plaintiffs seeking preliminary relief to demonstrate that irreparable injury is likely in the absence of an injunction." Issuing a preliminary injunction based only on a possibility of irreparable harm is inconsistent with the Court's characterization of injunctive relief as an extraordinary remedy that may only be awarded upon a clear showing that the plaintiff is entitled to such relief.

The Court also emphasized that "[a] preliminary injunction is an extraordinary remedy never awarded as of right" and that in each case, courts "must balance the competing claims of injury and must consider the effect on each party of the granting or withholding of the requested relief," paying "particular regard for the public consequences in employing the extraordinary remedy."

Circuit Variation on the Merits Prong

Note a circuit-level nuance: the Second Circuit applies a disjunctive formulation that is somewhat more flexible than a strict likelihood-of-success showing. "[T]he party seeking a preliminary injunction must establish that: (1) absent injunctive relief, it will suffer an irreparable injury; and (2) either (a) a likelihood of success on the merits or (b) sufficiently serious questions going to the merits to make them a fair ground for litigation and the balance of hardships tips in favor of the movant." Alliance Bond Fund, Inc. v. Grupo Mexicano De Desarrollo, S.A., 143 F.3d 6883 (persuasive — 2d Cir., outside your circuit unless this is a 2d Cir. matter). The Second Circuit also described irreparable harm as "[p]erhaps the single most important prerequisite for the issuance of a preliminary injunction." Attorneys should confirm which formulation their own circuit applies, since this affects how a "sufficiently serious questions" showing can substitute for a strong merits showing.

Rule 65 Procedural Requirements

Federal Rule of Civil Procedure 65 imposes additional mandatory procedural requirements:

1. Notice — "The court may issue a preliminary injunction only on notice to the adverse party."
2. Security/bond — "The court may issue a preliminary injunction or a temporary restraining order only if the movant gives security in an amount that the court considers proper to pay the costs and damages sustained by any party found to have been wrongfully enjoined or restrained. The United States, its officers, and its agencies are not required to give security."
3. Consolidation option — the court may advance the trial on the merits and consolidate it with the preliminary injunction hearing, but "must preserve any party's right to a jury trial."

Scope Limitation — No Prejudgment Asset Freezes for Money Damages

A critical limitation: in a pure action for money damages (no equitable claim, no lien, no pre-existing equitable interest), a federal court has no authority under its general equity powers to issue a preliminary injunction freezing a defendant's assets. In Grupo Mexicano De Desarrollo, S.A. v. Alliance Bond Fund, Inc., 527 U.S. 308 (1999) (binding — U.S. Supreme Court), the Court held that such relief was historically unavailable in equity: "Because such a remedy was historically unavailable from a court of equity, we hold that the District Court had no authority to issue a preliminary injunction preventing petitioners from disposing of their assets pending adjudication of respondents' contract claim for money damages." This distinguishes cases seeking equitable remedies (rescission, restitution, injunctive relief on the merits) — where asset-preserving preliminary injunctions remain available — from cases seeking only a money judgment.

Counterarguments / Practical Risks

• Opposing counsel's strongest move is often to attack the irreparable harm prong — courts (per Winter) require a likely, not merely possible, injury, and speculative or compensable-by-damages harm will defeat the motion.
• Grupo Mexicano is a powerful defense tool in any case framed as "just" a money-damages claim — if the movant cannot tie the requested freeze/injunction to an equitable claim or asserted interest in specific property, the court lacks authority to grant it, regardless of the equities.
• Bond/security is not waivable as a matter of course — defendants facing an improvidently granted injunction can recover on the bond, so movants should anticipate and brief an appropriate bond amount, and defendants should insist on an adequate one. Court Rule 65: Injunctions and Restraining Orders2

Practical Next Steps

• Frame the motion around the four Winter factors, leading with likelihood of success and a likely (not speculative) irreparable harm showing, with record evidence (declarations, not conclusory allegations).
• Confirm your circuit's specific articulation of the merits/hardship interplay (e.g., the Second Circuit's "serious questions" alternative) before drafting, since circuits differ in how rigidly they apply Winter.
• If the underlying claim is solely for money damages, assess exposure to a Grupo Mexicano challenge before seeking any asset-freezing injunction; consider instead state-law prejudgment attachment remedies under Rule 64.
• Propose a bond amount and be prepared to litigate it — courts will set security "in such sum as the court deems proper," and an undersized bond can be challenged post-hoc if the injunction turns out to be wrongful.

Searched our federal primary-law database (court rules) and federal case law (CourtListener) on preliminary injunction standards and bond/security requirements. Fed. R. Civ. P. 65(c)'s security provision was retrieved directly; no regulations were implicated. Authorities current as of the effective dates shown above; verify before filing.