An anti-suit injunction is a court order that stops a party from starting or continuing a lawsuit in another jurisdiction. The order works against the person, not the foreign court, because no US court has power to command a tribunal in another country. Instead, the judge controls a litigant subject to its personal jurisdiction, which effectively prevents that party from pursuing duplicative or abusive proceedings elsewhere. The remedy traces back to equity law and remains one of the sharpest tools available when the same dispute threatens to play out in two forums at once.
What a Court Looks at First
Before a federal court reaches the merits, the party seeking the order must clear a two-part gatekeeping inquiry. The parties in the US and foreign proceedings must be the same. A perfect match isn’t required, but the parties with a real stake in the outcome must overlap. The issues must also be substantially the same, meaning the US case’s resolution would effectively dispose of the foreign one. If either element is missing, the request fails regardless of how strong the underlying arguments are.
Because the order operates against a person rather than a foreign court, the issuing court must also have personal jurisdiction over the party it intends to restrain. Without that authority, the order has no legal force. This is straightforward when the restrained party is a US company or individual, and considerably more complex when the target is a foreign corporation with limited US contacts.
The Circuit Split on the Standard
Federal appellate circuits disagree on how readily these injunctions should issue, and the circuit where your case sits may be the single biggest factor in whether the motion succeeds.
The Liberal Approach
The Fifth, Seventh, and Ninth Circuits apply a more permissive standard that places modest weight on international comity and prioritizes judicial efficiency. A court will grant the injunction when the foreign litigation is duplicative and vexatious, or when allowing it to continue would produce inconsistent judgments or inequitable hardship. The practical question is whether letting the foreign case proceed would frustrate the domestic court’s ability to reach a complete and fair result.
Courts in these circuits typically apply the four-factor test first articulated in In re Unterweser Reederei, which asks whether the foreign litigation would frustrate a policy of the US forum, be vexatious or oppressive, threaten the court’s in rem or quasi in rem jurisdiction, or prejudice other equitable considerations.1United States Court of Appeals for the Ninth Circuit. Microsoft Corp. v. Motorola, Inc. The factors are disjunctive. Satisfying any one of them can justify the injunction.
The Conservative Approach
The First, Second, Third, Sixth, Eighth, and D.C. Circuits treat anti-suit injunctions as extraordinary remedies to be used sparingly. The court will issue the order only if the foreign proceeding would prevent US jurisdiction or threaten a vital US policy, and the domestic interests outweigh concerns of international comity.2United States Court of Appeals for the Fifth Circuit. No. 22-30168 The fact that a foreign lawsuit is expensive or duplicative is generally not enough on its own.
Some circuits in this camp, particularly the First and Second, apply a more flexible totality-of-the-circumstances analysis that weighs the parties’ conduct, the procedural posture of both cases, and whether a race to judgment is underway. The bar remains considerably higher than in the liberal circuits even under that variation.
Why Comity Makes Judges Hesitate
Comity, the mutual respect nations extend to each other’s courts and legal systems, is the main reason judges pause before issuing these orders. The injunction doesn’t technically command a foreign court to do anything, but the practical effect is the same: the foreign case stalls because one party can no longer participate. Foreign courts and governments view this as interference with their sovereignty, and US judges know that issuing the order today may invite retaliation against US litigants tomorrow.
The weight a court gives to comity depends heavily on its circuit’s approach. In the liberal circuits, comity is one factor among several and can be outweighed by domestic concerns. In the conservative circuits, comity operates almost as a presumption against the injunction. When a foreign nation has a strong independent interest in the dispute, such as a regulatory matter touching its domestic industry, even liberal-approach courts become more likely to deny the request.
Contractual Grounds: Forum Selection and Arbitration
Contractual provisions often provide the cleanest basis for an anti-suit injunction. When two parties agreed in writing to resolve disputes in a specific forum and one of them files suit somewhere else, the breach is straightforward and courts across all circuits are more willing to intervene.3George Mason Law Review. Global Standard Essential Patent Litigation: The Anti-Suit and Anti-Anti-Suit Injunctions The injunction enforces the bargain the parties struck.
Arbitration clauses work the same way. If a contract contains an agreement to arbitrate and one party instead files a lawsuit in a foreign court, US courts may issue an injunction to channel the dispute back into arbitration. The Second Circuit has grounded that authority in the court’s inherent equitable powers rather than any specific provision of the Federal Arbitration Act. These clauses also tend to reduce the comity concerns that otherwise make these injunctions difficult to obtain, because the argument shifts from “our court should hear this instead of yours” to “the parties already decided where this belongs.”
What the Motion Needs
A request for an anti-suit injunction is filed as either a preliminary injunction motion or a temporary restraining order, depending on how urgently the foreign proceedings need to be stopped. The application should identify every ongoing or threatened foreign action by case number, court name, and current status. Evidence establishing the overlap between the US and foreign cases is critical, since that is the gatekeeping inquiry the court addresses first.
Beyond overlap, the applicant has to show why the foreign litigation is harmful. That might include evidence that the opposing party filed abroad to gain tactical advantage, that duplicative discovery schedules would force the applicant to litigate in two countries at once, or that the foreign proceeding threatens to produce a judgment inconsistent with the US case. If a forum selection clause or arbitration agreement exists, the original contract should be front and center. Documenting the financial burden of parallel litigation strengthens the motion: duplicative legal fees, travel costs, and the expense of complying with conflicting discovery obligations all matter. The application should also include a proposed order spelling out exactly what the restrained party is prohibited from doing.
The Security Bond
Federal Rule of Civil Procedure 65(c) requires the party obtaining a preliminary injunction or TRO to post a security bond in an amount the court considers appropriate. The bond exists to compensate the restrained party if the injunction turns out to have been wrongfully issued.4Legal Information Institute (Cornell Law School). Rule 65 – Injunctions and Restraining Orders The US government and its agencies are exempt from this requirement.
The amount is left to the judge’s discretion. Courts sometimes set the bond at a nominal sum when the potential harm to the restrained party appears speculative or when the applicant can demonstrate a strong likelihood of success. When the restrained party faces significant financial exposure from being blocked out of the foreign proceeding, the bond can be substantial.
Serving the Order Abroad
Once a court signs the order, the restrained party must be served. Personal service inside the United States follows standard federal rules. When the party is overseas, the process becomes significantly more complicated.
If the restrained party sits in a country that has signed the Hague Service Convention, service must comply with that treaty’s requirements.5U.S. Department of State. Service of Process Many countries, including China, Japan, Mexico, and Germany, have formally objected to service by mail under Article 10(a) of the Convention. In those countries, service must go through the designated Central Authority, a process that can take weeks or months. That delay matters when the entire point of the injunction is to stop a foreign proceeding before it advances further.
What Happens When Someone Ignores the Order
A party who ignores an anti-suit injunction faces civil contempt, which federal courts have broad power to enforce. Civil contempt sanctions are designed to coerce compliance rather than punish, and they can include substantial daily fines that accumulate until the party complies. In one case involving parallel proceedings in Mexico, a federal judge imposed fines of $200,000 per day for violating a temporary restraining order by seeking an injunction in the foreign court.
Beyond fines, civil contempt can result in incarceration of indefinite duration. The restrained party stays in custody until they comply.6Federal Judicial Center. The Contempt Power of the Federal Courts For corporate parties, that typically means fines rather than imprisonment. For individuals, the threat of open-ended confinement makes these orders difficult to ignore.
Appealing the Decision
Unlike most pretrial rulings, an anti-suit injunction can be appealed immediately without waiting for a final judgment. Under 28 U.S.C. ยง 1292(a)(1), the courts of appeals have jurisdiction over interlocutory orders granting, modifying, refusing, or dissolving injunctions.7Office of the Law Revision Counsel. 28 USC 1292 – Interlocutory Decisions Notice of appeal must be filed within 30 days after entry of the order.8United States Court of Appeals for the Second Circuit. FRAP 4 – Appeal As Of Right – When Taken
The standard of review is abuse of discretion, which is highly deferential and gives the trial judge significant latitude. The appellate court will uphold the decision as long as it falls within a broad range of permissible conclusions and the judge didn’t make an error of law.1United States Court of Appeals for the Ninth Circuit. Microsoft Corp. v. Motorola, Inc. Factual findings are reviewed for clear error, and legal interpretations are reviewed fresh. Winning or losing at the trial level therefore carries enormous weight.
Anti-Anti-Suit Injunctions
When a US court issues an anti-suit injunction, the restrained party sometimes asks a foreign court to issue its own order blocking enforcement of the US injunction. This counter-move is called an anti-anti-suit injunction, and it has become increasingly common in cross-border patent and commercial disputes.3George Mason Law Review. Global Standard Essential Patent Litigation: The Anti-Suit and Anti-Anti-Suit Injunctions
The pattern escalates quickly. Court A tells a party to stop litigating in Court B. The party asks Court B to order them not to comply with Court A’s injunction. Court A may then respond with another order. No single court has authority to resolve the conflict, and each new order raises the tension between legal systems.
US courts treat requests for anti-anti-suit injunctions as extraordinary relief. The Second Circuit has held that preemptive injunctions designed to block foreign enforcement actions are generally unavailable.9NYU Journal of International Law and Politics. Anti-Enforcement Injunctions When a foreign court’s order directly threatens the US court’s jurisdiction over an ongoing proceeding, however, US judges have shown willingness to act defensively. Courts in Germany and the United Kingdom have been more aggressive with these tools, particularly in disputes involving standard essential patents, where competing injunctions from courts in different countries have become almost routine. A party caught between conflicting orders from two countries faces a genuinely impossible compliance situation, which is why these escalation cycles are viewed with alarm by courts and commentators worldwide.