What Does a Preliminary Injunction Do in a Lawsuit?

A preliminary injunction is an order from a court that prevents a party from performing specified acts during the litigation. It is considered an extraordinary remedy to preserve the status quo until a trial on the merits can be held. A preliminary injunction is usually granted early in the case, before a final decision is reached.

Preliminary injunctions are common in trade secret cases, certain business litigation disputes, and intellectual property cases. For example, a court may stop a former employee from using trade secrets or halt an alleged trademark infringement while the case proceeds.

An experienced civil litigation attorney can help you seek or oppose emergency court relief and help you move quickly to protect your rights.

How Preliminary Injunctions Function in Lawsuits

A preliminary injunction is temporary relief that ensures that the parties maintain the status quo in a civil litigation matter until the court decides on the merits of the case. The injunctive relief sought often asks a court to prevent an opposing party from taking a specific action or from continuing an action.

Preliminary injunctions can be used in any situation where a party would face irreparable harm if the status quo is not preserved. When a court issues a preliminary injunction, the non-moving party must be given notice and a chance to respond.

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Preliminary vs. Permanent Injunctions and TROs

A preliminary injunction does not determine who wins the case, but it pauses the action to protect the parties while the litigation continues. It pauses the case but does not resolve the matter.

Three related legal tools involve court-ordered relief designed to prevent harm before a case is fully resolved:

• Temporary restraining order (TRO). A TRO is a temporary injunction of a very short term. It is often issued on an expedited basis, and sometimes ex parte, meaning without notice to the other side, but it expires quickly (typically within 14 days under Rule 65 of the Federal Rules of Civil Procedure).
• Preliminary injunction. This type of injunction lasts through the lawsuit until the final ruling.
• Permanent injunction. An order that can be issued as part of the final judgment after the case is decided.

Together, these forms of relief give courts flexible tools to preserve the status quo and prevent irreparable harm at different stages of a case.

Preliminary Injunctions in State vs. Federal Courts

Preliminary injunctions are available in both state and federal courts. The federal courts follow Federal Rule of Civil Procedure 65, while each state has its own comparable rules and standards.

The goal of rules at the state and federal levels is to provide a legal mechanism that allows a party to seek early relief to prevent harm while the case proceeds. Whether a dispute belongs in state or federal court, preliminary injunctions are generally available as a tool of litigation.

What Is the Legal Basis for a Preliminary Injunction?

In federal court, courts generally apply the same four-factor test to preliminary injunctions and temporary restraining orders (TROs). However, TROs also have additional procedural requirements, such as specific showings about notice and the need for immediate relief.

When a party seeks an injunction, the party must prove the following:

• Substantial likelihood of success on the merits. The party seeking the injunction must be able to demonstrate, through evidence, that they are likely to win on the merits. The party must adequately state a legal claim against the defendant and support it with evidence, such as a verified complaint or affidavits, to demonstrate that the defendant’s conduct entitles the moving party to the injunctive relief sought.
• Irreparable harm. In general, irreparable harm means that an injury cannot be remedied by monetary damages or a final judgment on the merits. The irreparable injury requires a solution other than money damages.
• Balance of equities. The court must weigh the harm to the plaintiff against the harm to the defendants from being enjoined. Under this balancing test, courts generally hold that defendants do not suffer harm from being compelled to cease illegal conduct.
• Public interest. Courts often evaluate the underlying law that gives rise to the legal claims at issue in the case to determine whether a preliminary injunction is the proper relief, consistent with the public interest.

The court balances the relative weight of each factor in exercising its discretion, with the plaintiff’s likelihood of success on the merits being one of the most important factors.

The Preliminary Injunction Hearing

After a party files a motion for a preliminary injunction, the court will often hold a hearing. The hearing often serves as a “mini-trial” on the merits of the plaintiff’s case. The parties present evidence, call witnesses, and submit affidavits to the court to support their positions in the case.

The hearing is less formal than a final trial on the merits, and the court may rely on otherwise inadmissible evidence, including hearsay. FRCP 65(a)(2) states that admissible evidence provided during the preliminary injunction hearing becomes part of the trial record.

The movant must have the evidence it needs to establish its likelihood of success on the merits as quickly as possible. Expedited discovery may be allowed due to the circumstances of a preliminary injunction.

Use of Nationwide Injunctions: Supreme Court Ruling in Trump v. CASA, Inc.

In 2025, the U.S. Supreme Court issued a significant ruling in Trump v. Casa, Inc., a trio of cases that reshaped how broadly courts can apply certain injunctions.

The decision, authored by Justice Amy Coney Barrett, limited the use of universal or nationwide injunctions. These are orders that block a federal policy for everyone in the country, not just the people involved in the court case.

Courts can provide relief broad enough to fully protect the actual parties to the cause of action, but the court order generally cannot extend beyond that. That means an injunction cannot extend to people who are not part of the lawsuit.

Although this case did not address the underlying policy issue, the Court focused on the procedural order and the scope of the orders. As a result of the CASA ruling, relief for parties may need to be more narrowly tailored to the specific parties in the lawsuit, which can impact case strategy, including class actions and who joins.

Why You Need a Strategic Lawyer

Unless you have litigation experience, seek legal help when you need to seek or oppose a preliminary injunction. This type of legal proceeding for injunctive relief is complex and fast-moving, and the law continues to evolve, so knowledgeable guidance is essential.

There are many tasks required for the four-factor test, such as quickly gathering evidence and handling the bond requirements, to name a few. Procedures vary from court to court, so it is recommended that you hire an experienced civil litigation attorney to guide you.