An antitrust lawsuit is a legal action brought to stop business conduct that unfairly eliminates or suppresses competition, such as price-fixing, illegal monopolization, or mergers that would dominate a market. These cases can be filed by federal agencies, state attorneys general, or private businesses and consumers who have been harmed. Penalties range from prison sentences and corporate fines to damage awards that federal law automatically triples.
Three federal statutes do most of the work. The Sherman Act of 1890 outlaws agreements that restrain trade and makes it a felony to monopolize a market. The Clayton Act of 1914 targets specific practices the Sherman Act did not reach cleanly, including anticompetitive mergers, exclusive dealing, and price discrimination, and it gives private parties the right to sue for triple damages. The Federal Trade Commission Act, also from 1914, created the FTC and authorized it to challenge “unfair methods of competition,” though only the FTC itself can enforce that statute.1Office of the Law Revision Counsel. 15 USC 3503 – Antitrust Law Defined
What Conduct Can Trigger a Lawsuit
Antitrust law does not punish companies for being aggressive or successful. It targets specific categories of behavior that harm the competitive process itself.
Agreements Among Competitors
When companies that are supposed to compete instead agree not to, that is the most straightforward violation. The DOJ’s Antitrust Division criminally prosecutes three forms of collusion: price-fixing (agreeing on what to charge), bid-rigging (coordinating who wins a contract), and market allocation (dividing up customers or territories).2United States Department of Justice. Criminal Enforcement
These agreements are “per se” illegal under Section 1 of the Sherman Act. The government does not have to prove the scheme actually raised prices or hurt consumers. The agreement itself is the crime. Failed or one-sided attempts — one company solicits a deal and the other refuses — are generally not prosecutable under Section 1, though they often draw federal scrutiny.3U.S. Department of Justice. Federal Antitrust Crime: A Primer for Law Enforcement Personnel
Unlawful Monopolization
Being the dominant company in a market is legal. Winning that position by building better products or operating more efficiently is exactly what competition is supposed to reward. The violation happens when a company uses anticompetitive tactics to get or keep its dominance — predatory pricing meant to bankrupt smaller rivals, exclusive contracts designed to lock competitors out of distribution, and similar conduct.4Office of the Law Revision Counsel. 15 USC 2 – Monopolizing Trade a Felony; Penalty
Courts look at two things. First, does the company actually have monopoly power in a defined market? As a rough benchmark, companies with over 70% market share are likely considered monopolists, those below 50% generally are not, and the 50% to 70% range is a gray zone where other factors matter, particularly whether barriers to entry keep new competitors from emerging. Second, did the company gain or protect that power through conduct that goes beyond competing on the merits? Both elements must be present.
Anticompetitive Mergers
The Clayton Act prohibits any merger whose effect “may be substantially to lessen competition, or tend to create a monopoly.”5United States Department of Justice. 2023 Merger Guidelines Overview Regulators do not need to prove a merger will definitely harm competition, only that it creates a meaningful risk. Large transactions must be reported in advance to both the FTC and DOJ under the Hart-Scott-Rodino Act, and the parties have to wait out a review period before closing.6Federal Trade Commission. Premerger Notification Program If reviewers see competitive problems, the agencies can sue to block the deal, demand divestitures, or negotiate conditions.
Who Can File an Antitrust Lawsuit
Enforcement comes from three directions, and a single scheme can draw suits from all of them at once.
Federal Agencies
The DOJ’s Antitrust Division is the only body that can bring criminal antitrust charges. It prosecutes price-fixing, bid-rigging, and market allocation as felonies, seeking prison time and fines against both corporations and the individual executives involved.2United States Department of Justice. Criminal Enforcement On the civil side, both DOJ and the FTC can sue to block mergers or halt ongoing anticompetitive practices. In merger reviews, both agencies receive HSR filings but only one handles the review, splitting responsibility informally by industry expertise.
Before any lawsuit is filed, the agencies have serious investigative tools. The FTC can issue civil investigative demands that compel companies to produce documents, answer written questions, and give testimony.7Federal Trade Commission. A Brief Overview of the Federal Trade Commission’s Investigative, Law Enforcement, and Rulemaking Authority In merger cases, either agency can issue a “second request” for additional documents and data, which extends the waiting period and often takes months to satisfy. Compliance costs alone can run into tens of millions of dollars, which is one reason many deals are restructured or abandoned before a courtroom is ever involved.
State Attorneys General
State attorneys general can sue under federal antitrust law on behalf of residents who were harmed. This parens patriae authority lets a state’s top lawyer seek money for consumers without each consumer having to file a separate case.8Office of the Law Revision Counsel. 15 USC 15c – Actions by State Attorneys General Most states also have their own antitrust statutes that mirror federal law, which gives attorneys general a second avenue. State and federal authorities often coordinate, particularly on cases involving national markets.
Private Businesses and Consumers
Private suits make up a large share of antitrust litigation. Any person or business injured by an antitrust violation can sue in federal court and recover three times their actual damages, plus attorney’s fees and costs.9Office of the Law Revision Counsel. 15 USC 15 – Suits by Persons Injured That treble-damages provision is what makes private enforcement financially viable; without it, many plaintiffs could not justify the expense of taking on a large corporation.
Not every injured party has the right to sue. Federal courts require “antitrust standing,” which looks past the fact that a plaintiff lost money. Judges weigh whether the injury is the type Congress intended to prevent, how directly the harm flows from the violation, and whether more direct victims are better positioned to bring the case.10Justia U.S. Supreme Court Center. Associated General Contractors v. Carpenters, 459 U.S. 519 (1983) Remote or speculative injuries usually fail that test.
There is also a significant limitation for consumers who buy down the supply chain. Under Illinois Brick Co. v. Illinois, only direct purchasers — the parties who bought from the company that violated the law — can recover treble damages in federal court.11Justia U.S. Supreme Court Center. Illinois Brick Co. v. Illinois, 431 U.S. 720 (1977) A consumer who paid inflated prices at a store because the manufacturer ran a price-fixing scheme likely cannot sue under federal law, because the direct purchase was from the retailer. Many states have passed “Illinois Brick repealer” statutes that let indirect purchasers bring claims under state antitrust law.
How the Case Moves Forward
Antitrust cases vary enormously based on who files and what the alleged conduct is, but most follow a recognizable arc.
Investigation
Government cases almost always begin with a long investigation before any complaint is filed. The DOJ or FTC may learn of possible violations through industry tips, whistleblowers, leniency applications from inside a cartel, or routine market monitoring. For mergers, the HSR filing itself opens the review. The agency then issues subpoenas or civil investigative demands to gather documents, data, and testimony. Second requests in merger cases can add months.
Private cases start differently. A business suspicious of a competitor may hire economists and lawyers to analyze a market before suing. Consumer class actions frequently piggyback on government work: once the DOJ announces indictments for price-fixing, plaintiffs’ firms file civil suits seeking treble damages based on the same conduct.
Filing and Litigation
Once a complaint is filed, the case proceeds like other federal litigation. The defendant answers, both sides engage in discovery, and the case moves toward trial. Antitrust discovery is notoriously expensive because the key evidence — pricing data, internal communications, market studies — is voluminous and technically complex. Expert economists are central, offering competing analyses of market definition, competitive effects, and damages.
Private class actions add a hurdle. The plaintiffs must convince the court to certify a class before the case can proceed on behalf of a group. That certification fight is often the hardest-fought phase, because a company facing one plaintiff’s damages may be willing to try the case, while a company facing thousands of purchasers has far more at stake.
Settlement and Consent Decrees
Most antitrust cases settle. When the DOJ settles a civil case, the agreement is called a consent decree, formally a “Final Judgment.” These are not handshake deals. The Antitrust Procedures and Penalties Act, known as the Tunney Act, requires the DOJ to publish the proposed settlement and a competitive impact statement in the Federal Register, accept public comments for at least 60 days, and then convince the court that the settlement is in the public interest before a judge can enter it.12United States Department of Justice. Explanation of Consent Decree Procedures FTC settlements go through the agency’s own administrative process. Private cases settle through ordinary negotiation, often ending in a cash payment and sometimes an agreement to change future business practices.
Penalties and Remedies
The consequences of losing depend on whether the case is criminal or civil, and on who brought it.
Criminal Penalties
Sherman Act violations are felonies. A convicted corporation faces fines up to $100 million per offense. An individual, typically a senior executive who personally participated, faces up to $1 million in fines and up to 10 years in prison.13Office of the Law Revision Counsel. 15 USC 1 – Trusts, Etc., in Restraint of Trade Illegal; Penalty The same structure applies to criminal monopolization charges.4Office of the Law Revision Counsel. 15 USC 2 – Monopolizing Trade a Felony; Penalty
Those caps can be exceeded. When the gain from the conspiracy or the loss it caused victims is large enough, courts can impose fines up to twice the gross gain or twice the gross loss, whichever is greater. The largest corporate antitrust fines in history have been calculated that way, often reaching hundreds of millions of dollars. Convicted individuals may also be suspended or barred from doing business with the federal government.3U.S. Department of Justice. Federal Antitrust Crime: A Primer for Law Enforcement Personnel
Treble Damages in Private Suits
A winning private plaintiff recovers three times the actual damages sustained, plus costs and a reasonable attorney’s fee.9Office of the Law Revision Counsel. 15 USC 15 – Suits by Persons Injured Courts may also award prejudgment interest on actual damages from the filing date through judgment. Congress built the math this way deliberately to encourage private enforcement alongside the government’s.
Injunctions and Divestiture
Money is not the only remedy. Courts can order companies to stop a specific practice — halt a pricing scheme, end an exclusive dealing arrangement, or abandon a proposed merger. In monopolization cases, courts sometimes order structural remedies, requiring a company to sell off business units or assets to restore competition. A company that illegally absorbed a competitor can be forced to sell the acquired business to a new, independent owner.
How Long You Have to Sue
A private antitrust plaintiff has four years from the date the cause of action accrued to file suit.14Office of the Law Revision Counsel. 15 USC 15b – Limitation of Actions Miss that deadline and the claim is permanently barred. For ongoing conspiracies, the clock typically resets with each new act that causes injury, but the window is still tight, especially since violations are often concealed for years before anyone discovers them.
One important exception: when the federal government brings its own criminal or civil antitrust case, the clock pauses for every related private claim based on the same conduct. It stays frozen for the duration of the government case and for one year after it ends, giving private plaintiffs extra time to assemble their own suits.15Office of the Law Revision Counsel. 15 USC 16 – Judgments That tolling rule is why a wave of private treble-damages suits usually follows right after the DOJ announces guilty pleas in a cartel case.
Where Antitrust Law Does Not Reach
Some conduct that looks anticompetitive is protected by statute or legal doctrine, and recognizing those zones matters before anyone considers suing.
The Clayton Act expressly provides that labor unions and agricultural cooperatives are not illegal combinations in restraint of trade.16Office of the Law Revision Counsel. 15 USC 17 – Antitrust Laws Not Applicable to Labor Organizations Without that exemption, collective bargaining itself could be characterized as a conspiracy to fix wages.
Under the state action doctrine, when a state government deliberately displaces competition with a regulatory scheme, the resulting conduct is immune from federal antitrust liability. The doctrine traces to the Supreme Court’s 1943 decision in Parker v. Brown. Private companies can also claim this immunity, but only if the state has clearly articulated a policy to displace competition and actively supervises the conduct.
Under the Noerr-Pennington doctrine, companies that lobby legislatures, petition regulators, or file lawsuits seeking anticompetitive outcomes are generally immune, because the right to petition the government is constitutionally protected. The exception is “sham” petitioning: a lawsuit or regulatory filing that is objectively baseless and really aimed at interfering with a competitor loses the protection.