Antitrust and regulation in the United States

Lessons 5 to 9 showed that market power raises prices above marginal cost, that a few firms can sometimes sustain high prices without explicit agreement, and that incumbents can make threats and commitments that deter entry. Societies respond with antitrust law, which prohibits the most harmful conduct and reviews mergers that would reduce competition, and with economic regulation, which sets prices or terms of service in industries where competition cannot work well. Managers need to understand both. Antitrust law shapes which acquisitions are possible, how pricing and distribution agreements can be written, what can be said to competitors and how dominant firms may behave. Getting it wrong can mean criminal prosecution, treble damages in private lawsuits and blocked deals. This lesson covers the American framework, which rests on statutes more than a century old, and how its economics have been applied in recent cases.

The Sherman, Clayton and FTC Acts

American antitrust law rests on three statutes. The Sherman Act of 1890 prohibits, in section 1, contracts, combinations and conspiracies in restraint of trade and, in section 2, monopolization and attempts to monopolize. The Clayton Act of 1914 prohibits, in section 7, mergers and acquisitions whose effect may be substantially to lessen competition or tend to create a monopoly, and it allows private parties to sue for three times their damages. The Federal Trade Commission Act of 1914 created the FTC and prohibits unfair methods of competition. Enforcement is shared between the Antitrust Division of the Department of Justice, which alone can bring criminal cases, and the FTC, which brings civil cases. State attorneys general also enforce federal and state antitrust laws, and private lawsuits, including class actions, are a major part of enforcement.

Courts have interpreted these statutes through a long line of cases. Some agreements between competitors, such as price fixing, bid rigging and market allocation, are illegal per se: no justification is accepted, and the Antitrust Division prosecutes them as felonies punishable by large fines and prison. Most other business practices are judged under the rule of reason, which weighs a practice's harm to competition against its benefits. Since the late 1970s, courts have used the consumer welfare standard, focusing on effects on price, output, quality and innovation. Recent enforcement leaders have argued for broader attention to labor markets, potential competition and the structure of digital markets, and the Antitrust Division has prosecuted wage-fixing and no-poach agreements among employers.

Cartels and agreements between competitors

Section 1 of the Sherman Act makes price fixing, bid rigging and market allocation among competitors felonies. Corporations can be fined up to 100 million dollars or twice the gain or loss from the offense, and individuals can be imprisoned for up to ten years. The Antitrust Division's leniency program gives the first company to report a cartel and cooperate immunity from prosecution, and it has been the source of many of the largest cases, including the international cartels discussed in Lesson 6. Purchasers harmed by cartels can sue for treble damages, so the total cost to a cartel member often far exceeds the criminal fine.

For managers, the practical rules are clear. Never discuss prices, margins, bids, customers, territories, capacity plans or wages with competitors, including at trade association meetings and social events. If a competitor raises these topics, leave the conversation and report it to counsel. Be careful with benchmarking exercises and information exchanges, which are legitimate only when data are aggregated, historical and managed by a third party. Joint ventures and strategic alliances between competitors can be lawful and efficient, for example in research, purchasing or shared infrastructure, but they need legal review and clear limits on the information shared. Pricing algorithms add a new dimension: firms are responsible for the outcomes of the algorithms they use, and sharing a common pricing tool with competitors can raise the same concerns as direct communication.

Merger review

Mergers can create value through economies of scale and scope, complementary capabilities and better management, but horizontal mergers between competitors can also create or strengthen market power. Competition authorities review mergers to prevent those likely to substantially lessen or prevent competition. The analysis follows a common economic structure in most jurisdictions: define the relevant market, measure concentration, assess whether the merger would allow the combined firm to raise prices unilaterally or would make coordination among the remaining firms easier, and consider entry, buyer power and efficiencies.

Market definition uses the hypothetical monopolist test: the relevant market is the smallest group of products and geographic area in which a hypothetical sole supplier could profitably impose a small but significant and non-transitory increase in price, typically 5 %. If customers would switch to products outside the group in large enough numbers to make the increase unprofitable, the group is too narrow. The critical loss analysis from Lesson 3's elasticity concepts makes this concrete: a 5 % price increase is profitable if the fraction of sales lost is below the critical loss, which equals the price increase divided by the sum of the increase and the margin.

Concentration is measured by the Herfindahl–Hirschman Index, the sum of the squared market shares of all firms, with shares in percentage points. A market with one firm has an index of 10,000; a market with ten equal firms has an index of 1,000. The increase in the index caused by a merger of firms A and B equals twice the product of their shares.

The 2023 Merger Guidelines issued jointly by the Department of Justice and the FTC presume that a merger substantially lessens competition if it increases the index by more than 100 and results in an index above 1,800, or if the merged firm has a market share above 30 % and the increase exceeds 100. The guidelines also address vertical mergers, serial acquisitions, platforms, labor markets and the loss of potential competition, and the agencies continued to apply them after the 2025 change of administration. Under the Hart–Scott–Rodino Act, transactions above a size threshold, adjusted each year, must be notified before closing, with a 30-day waiting period that can be extended by a request for additional information, known as a second request.

# Merger screen: concentration index and the structural presumption
def hhi(shares):
    return sum(s ** 2 for s in shares)

def screen(shares, a, b):
    pre = hhi(shares)
    merged = [s for i, s in enumerate(shares) if i not in (a, b)] + [shares[a] + shares[b]]
    post = hhi(merged)
    delta = post - pre
    combined = shares[a] + shares[b]
    presumed = delta > 100 and (post > 1800 or combined > 30)
    return pre, post, delta, combined, presumed

markets = {
    'Regional grocery (Fairway buys #4)':     ([28, 22, 18, 12, 10, 10], 0, 3),
    'Steel coil distribution (#3 buys #6)':   ([30, 25, 15, 15, 10, 5], 2, 5),
    'Forecasting software (Kestrel buys #6)': ([20, 15, 12, 10, 8, 6, 5, 5, 5, 5, 5, 4], 5, 4),
}
for name, (shares, a, b) in markets.items():
    pre, post, delta, comb, pres = screen(shares, a, b)
    print(f"{name:40s} pre {pre:5d}  post {post:5d}  change {delta:4d}  share {comb:3d} %  presumed: {'yes' if pres else 'no'}")

# Critical loss for a 5 % price increase at different margins
for margin in (0.2, 0.4, 0.6):
    print(f"Margin {margin:.0%}: critical loss = {0.05 / (0.05 + margin):.1%} of sales")

Regional grocery (Fairway buys #4)       pre  1936  post  2608  change  672  share  40 %  presumed: yes
Steel coil distribution (#3 buys #6)     pre  2100  post  2250  change  150  share  20 %  presumed: yes
Forecasting software (Kestrel buys #6)   pre  1110  post  1206  change   96  share  14 %  presumed: no
Margin 20%: critical loss = 20.0% of sales
Margin 40%: critical loss = 11.1% of sales
Margin 60%: critical loss = 7.7% of sales

The code screens three hypothetical deals. Fairway's purchase of the fourth-largest regional grocer raises the index by 672 to well above 1,800 and gives a combined share of 40 %, so it is presumed harmful; Fairway would need to show that the market is broader than assumed, for example because discount and online grocers constrain prices, or offer to divest stores where overlap is greatest. The distributor deal raises the index by 150 and creates a 20 % share, but the post-merger index of 2,250 exceeds 1,800, so the presumption applies. Kestrel's small acquisition in fragmented software raises the index by 96 and falls below the threshold. The critical loss lines show that high-margin businesses need to lose only a small share of sales for a price increase to fail, which is why market definition in high-margin industries is often contested.

Recent American merger cases show the analysis at work. The FTC blocked or abandoned several large deals in groceries, health care and consumer products, including Kroger's proposed acquisition of Albertsons, which a federal court enjoined in December 2024 after finding that it would likely harm competition among supermarkets; the FTC's complaint had also alleged harm to unionized grocery workers. The agencies have also challenged hospital mergers, technology acquisitions of potential competitors and serial roll-ups of physician practices by private equity firms, showing that labor markets and acquisitions of small competitors are now part of merger review.

Monopolization

Section 2 of the Sherman Act prohibits monopolization, which courts define as possessing monopoly power in a relevant market and acquiring or maintaining it through exclusionary conduct rather than through a superior product, business acumen or historic accident. Being a monopolist is not illegal; excluding rivals by means other than competition on the merits is. Exclusionary conduct can include predatory pricing below cost with a dangerous probability of recouping losses, exclusive contracts that foreclose a substantial share of the market, tying, refusals to deal in narrow circumstances and acquisitions of nascent rivals. In August 2024, a federal court held that Google had unlawfully maintained a monopoly in general search through exclusive default agreements, and the remedies decision in 2025 barred exclusive contracts and required some sharing of data with rivals, illustrating how section 2 applies to digital markets.

Game theory explains why authorities are cautious about predatory pricing claims. Lesson 8 showed that a threat to fight entry is often not credible, because fighting is costly for the incumbent. Low prices are usually good for customers, and a firm that cuts prices in response to entry is usually competing, not predating. Predation becomes plausible when the incumbent can recoup its losses later, for example because barriers to re-entry are high, and when the price is below a measure of avoidable or marginal cost. The analysis therefore combines cost tests from Lesson 4 with an assessment of market structure from Lessons 5 and 6.

Vertical restraints and distribution

Agreements between firms at different levels of the supply chain, such as exclusive dealing, territorial restrictions and resale price maintenance, are judged under the rule of reason. In the Leegin decision of 2007, the Supreme Court overturned the century-old per se rule against minimum resale price maintenance, recognizing that it can encourage retailers to provide service and prevent free-riding, though some states still treat it as illegal. Tying, in which a seller requires buyers of one product to buy another, can be unlawful when the seller has market power in the tying product. Daniel was advised that Northfield could suggest resale prices to its aftermarket distributors in both countries but should avoid agreements fixing minimum prices and should review state law where it sells.

Economic regulation

Where competition cannot work, because a market is a natural monopoly or because firms control essential facilities such as pipelines, transmission lines or local networks, governments regulate prices and service terms directly. Lesson 5 introduced the two main approaches. Under cost-of-service or rate-of-return regulation, the regulator sets prices to cover operating costs plus a fair return on the rate base, the depreciated value of invested capital. This assures investors and encourages investment but weakens incentives to cut costs, and it can encourage over-investment in capital, a tendency analyzed by Harvey Averch and Leland Johnson in 1962. Under price-cap or incentive regulation, the regulator sets a price path, often inflation minus a productivity factor, and the firm keeps the savings if it beats it. This strengthens cost discipline but risks quality cuts, so regulators add service quality standards.

In the United States, state public utility commissions set electricity, natural gas and water distribution rates, the Federal Energy Regulatory Commission regulates interstate transmission, wholesale electricity markets and interstate pipelines, and the Federal Communications Commission regulates telecommunications. Many states have adopted performance-based ratemaking for utilities, combining multi-year rate plans with incentives tied to reliability and customer service. Owen deals with FERC on pipeline tariffs for Prairie Ridge's gas transported through the United States and with state commissions on electricity costs at its operations.

Regulation also extends beyond prices. Health and safety, environmental and financial regulation correct externalities and information problems discussed in Lessons 1 and 9. Hana's work at Lakeview involves rules on clinical standards, privacy of health information and reimbursement rates. Managers can use economics to engage constructively with regulators: estimating the costs and benefits of proposed rules, proposing alternatives that achieve the regulator's goals at lower cost, and understanding how regulators trade off affordability, reliability and investment.