Antitrust Law Guide: Sherman Act, Clayton Act, and Competition Regulation
The most dangerous word in business is “monopoly.” Even the mere accusation of anticompetitive conduct can crater a company’s stock price, trigger years of litigation, and attract the attention of enforcers with the power to break up your company. Microsoft learned this in the 1990s. AT&T learned it in the 1980s. Standard Oil learned it in 1911. Antitrust law is the legal framework that keeps markets competitive, and every business decision—from pricing to partnerships to mergers—operates within its shadow.
Antitrust law in the United States rests on three federal statutes: the Sherman Act of 1890, the Clayton Act of 1914, and the Federal Trade Commission Act of 1914. These laws prohibit anticompetitive conduct, mergers that substantially lessen competition, and unfair methods of competition. The Department of Justice Antitrust Division and the Federal Trade Commission (FTC) share enforcement authority, with overlapping jurisdiction that requires coordination through a clearance process.
The Sherman Act
Section 1: Contracts in Restraint of Trade
Section 1 of the Sherman Act prohibits “every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States.” The Supreme Court has interpreted this language to prohibit only unreasonable restraints. Per se illegal restraints—those that are always illegal—include horizontal price-fixing, bid-rigging, market allocation, and group boycotts. Rule of reason analysis applies to conduct that may have procompetitive justifications.
Price-Fixing
Price-fixing agreements among competitors are per se illegal under United States v. Socony-Vacuum Oil Co. (1940). The agreement need not be explicit—tacit coordination among competitors can violate the Sherman Act if it involves communication. Information exchanges that facilitate price coordination may also violate Section 1. The DOJ prosecutes price-fixing as a criminal offense, with penalties including prison sentences of up to 10 years and corporate fines up to $100 million.
Market Allocation
Agreements among competitors to divide markets by geography, customer type, or product line are per se illegal. The Supreme Court in Palmer v. BRG of Georgia, Inc. (1990) held that a market allocation agreement between two bar review courses was per se illegal. The DOJ Leniency Program encourages participants in cartel activity to self-report in exchange for amnesty from criminal prosecution.
Section 2: Monopolization
Section 2 of the Sherman Act prohibits monopolization, attempted monopolization, and conspiracies to monopolize. Monopolization requires monopoly power in a relevant market plus willful acquisition or maintenance of that power. The offense of monopolization does not require that the monopoly was obtained illegally—only that it is maintained through exclusionary conduct.
Predatory Pricing
Predatory pricing occurs when a firm prices below cost to drive competitors out of the market and then raises prices to recoup losses. The Supreme Court in Brooke Group Ltd. v. Brown & Williamson Tobacco Corp. (1993) required proof that prices are below an appropriate measure of cost and that the predator has a dangerous probability of recouping its investment. This high standard makes predatory pricing claims difficult to prove.
The Clayton Act
Merger Review
Section 7 of the Clayton Act prohibits mergers and acquisitions where the effect “may be substantially to lessen competition, or to tend to create a monopoly.” The Hart-Scott-Rodino Antitrust Improvements Act of 1976 requires parties to certain mergers to file premerger notification with the DOJ and FTC and observe a waiting period before closing. The HSR threshold adjusts annually—in 2024, transactions valued at over $119.5 million require filing.
Horizontal Mergers
Horizontal mergers between direct competitors receive the closest antitrust scrutiny. The DOJ and FTC Horizontal Merger Guidelines consider market concentration, the potential for coordinated effects, and the potential for unilateral effects (where the merged firm can profitably raise prices without coordination). High market concentration, measured by the Herfindahl-Hirschman Index (HHI), raises presumption of anticompetitive effect.
Vertical Mergers
Vertical mergers between firms at different levels of the supply chain face less stringent review but can raise concerns about foreclosure of rivals, raising rivals’ costs, and access to competitively sensitive information. The FTC successfully challenged vertical mergers in AT&T/Time Warner (2018) and Nvidia/Arm (2022). The 2020 Vertical Merger Guidelines were withdrawn in 2021, creating uncertainty about the analytical framework.
Interlocking Directorates
Section 8 of the Clayton Act prohibits interlocking directorates—the same person serving as director of two competing corporations—when the corporations are competitors and each has capital, surplus, and undivided profits exceeding approximately $45 million. This prohibition applies to horizontal competitors regardless of market share and is strictly enforced by the Antitrust Division.
Unfair Methods of Competition
Section 5 of the FTC Act prohibits “unfair methods of competition in or affecting commerce” and “unfair or deceptive acts or practices in or affecting commerce.” The FTC has increasingly used Section 5 to challenge conduct that may not violate the Sherman Act or Clayton Act. The 2022 FTC Policy Statement on Section 5 emphasized standalone authority to address incipient violations and conduct that violates the spirit of the antitrust laws.
Robinson-Patman Act
The Robinson-Patman Act of 1936 prohibits price discrimination that substantially lessens competition between purchasers. Sellers must charge proportionally equal prices to competing buyers for goods of like grade and quality. Defenses include cost justification, changing market conditions, and meeting competition. Enforcement of the Robinson-Patman Act declined in the late twentieth century but has seen renewed interest in the 2020s.
Antitrust Remedies
Government Enforcement
The DOJ and FTC can seek injunctive relief to prevent anticompetitive conduct or to require divestiture of assets in merger cases. Structural remedies—requiring the divestiture of assets or business units—are preferred in merger cases. Behavioral remedies—requiring ongoing compliance and reporting—are more common in conduct cases. The DOJ can also seek criminal penalties for hard-core cartel conduct.
Private Actions
Private plaintiffs may sue for treble damages and attorneys’ fees under Section 4 of the Clayton Act. Indirect purchasers—those who bought from a direct purchaser that was overcharged—face barriers under Illinois Brick Co. v. Illinois (1977), which limits standing to direct purchasers. Class actions are common in price-fixing cases. The FTC and DOJ encourage private enforcement as a supplement to government resources.
International Antitrust Enforcement
Antitrust enforcement is increasingly global. The European Commission’s Directorate-General for Competition enforces Articles 101 and 102 of the Treaty on the Functioning of the European Union, which prohibit anticompetitive agreements and abuse of dominant position. The EU has imposed some of the largest antitrust fines in history, including a €4.3 billion penalty against Google for Android antitrust violations. The European Digital Markets Act imposes additional obligations on large online platforms designated as gatekeepers.
China’s Anti-Monopoly Law, amended in 2022, expanded enforcement authority against monopolistic conduct. The Japan Fair Trade Commission, the UK Competition and Markets Authority, and other national competition authorities coordinate through the International Competition Network. Mergers and conduct with international dimensions must satisfy the antitrust requirements of every jurisdiction where the business operates. Global companies typically employ antitrust counsel familiar with multiple enforcement regimes.
Antitrust and the Digital Economy
Digital markets present unique antitrust challenges. Network effects, data advantages, and multi-sided platform dynamics create markets that tend toward concentration. The House Judiciary Antitrust Subcommittee’s 2020 investigation concluded that Amazon, Apple, Facebook, and Google held monopoly power in key market segments. The report recommended structural separations, interoperability requirements, and non-discrimination rules for dominant platforms.
The European Digital Markets Act (DMA) imposes proactive obligations on designated gatekeeper platforms, including prohibitions on self-preferencing, restrictions on combining personal data across services, and requirements for interoperability and data portability. The United States has not enacted comparable legislation, though the American Innovation and Choice Online Act and the Open App Markets Act were proposed in Congress. The FTC and DOJ have brought antitrust cases against Google for search monopolization and against Meta for anticompetitive acquisitions.
Frequently Asked Questions
What is the difference between per se and rule of reason violations? Per se violations are always illegal regardless of justification. Price-fixing, bid-rigging, and market allocation among competitors are per se violations. Rule of reason violations require analysis of procompetitive justifications and anticompetitive effects. Most vertical restraints and monopolization claims are evaluated under the rule of reason.
Do I need to report my merger to the government? Transactions valued at over $119.5 million (2024 threshold) require HSR filing if the parties meet certain size thresholds. Failure to file can result in penalties of up to $51,744 per day. Even transactions below the threshold may be challenged if they substantially lessen competition.
Can my company be convicted of antitrust violations? Yes. Corporations face criminal penalties for Sherman Act violations, including fines up to $100 million. Individual employees face prison sentences up to 10 years. The DOJ Leniency Program reduces penalties for companies that self-report. Corporate compliance programs can mitigate penalties but do not immunize illegal conduct.
How do I know if my pricing practices violate antitrust law? Pricing practices that involve agreement with competitors (price-fixing), pricing below cost (predatory pricing), or price discrimination that harms competition (Robinson-Patman Act) may violate antitrust law. Independent pricing decisions do not violate the Sherman Act even if competitors charge similar prices. See our corporate governance guide for board-level antitrust compliance responsibilities.