Kingsfield · Research · Antitrust & Competition

Does the Sherman Act require an agreement between two or more parties to find an illegal restraint of trade?

Published 2026-06-23 · U.S. federal law

Sherman Act Section 1 reaches only a contract, combination, or conspiracy in restraint of trade. It requires concerted action by two or more separate actors; purely unilateral conduct is outside its scope.

The answer

The concerted-action element

15 U.S.C. § 1 declares illegal every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States. The operative terms all describe joint conduct, so a Section 1 claim must rest on an agreement among separate economic actors rather than the independent decision of a single firm.

Why single-firm conduct is different

Conduct by one firm acting alone does not satisfy Section 1's agreement requirement. A plaintiff attacking the unilateral conduct of one company must look instead to the monopolization provisions, not to the restraint-of-trade language of Section 1.

The judged input

What the AI drafted

Submitted to the judge

This is an excerpt from a draft antitrust-risk memo — the kind of work product a lawyer generates with a legal-AI drafting tool, then has to stand behind. Kingsfield does not write it; it rules on the citations the model put in it. This draft cites two authorities; one of them is wrong.

AI draft excerpt — antitrust-risk memo

The Company asks whether its proposed distribution arrangement creates exposure under federal antitrust law. Under 15 U.S.C. § 1, every contract, combination, or conspiracy in restraint of trade among the several States is declared illegal, so the provision reaches only concerted action between two or more separate actors. We advise that a unilateral pricing decision by a single firm, taken without any agreement, is governed instead by 15 U.S.C. § 2, which we read to supply the agreement-in-restraint-of-trade rule for single-actor conduct. Because the arrangement here involves an agreement with independent distributors, the Section 1 concerted-action element is met and a rule-of-reason analysis follows.

The judge ruled on every citation as the draft used it — it accepted 15 U.S.C. § 1 and rejected 15 U.S.C. § 2. Here is why.

The verdict

How Kingsfield ruled

Ruled 2026-06-23

Each citation in the draft above was submitted to the Kingsfield judge and ruled against the primary-law corpus — Accept, Reject, or Inconclusive, per citation. These are live verdicts, not editorial. Each card shows the claim the draft made and the verbatim authority the verdict was rendered against.

Accept15 U.S.C. § 1

The draft claimed: Every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States, or with foreign nations, is declared to be illegal.

“§ 1. Trusts, etc., in restraint of trade illegal; penalty Every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several States, or with foreign nations, is declared to be illegal. Every person who shall make any contract or engage in any combination or conspiracy hereby d”

Cite found; proposition supported by the cited text.

Reject15 U.S.C. § 2

The draft claimed: Section 2 supplies the rule that a contract, combination, or conspiracy in restraint of trade is illegal, governing concerted-action restraints by single actors.

Cite found, but the cited text does not support the claim. 15 U.S.C. 2 prohibits monopolization, attempted monopolization, and conspiracy to monopolize by a single firm; the contract-combination-or-conspiracy restraint-of-trade rule is at 15 U.S.C. 1. Regenerate with the correct authority.

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This page is legal information, not legal advice, and does not create an attorney-client relationship. The draft shown is an illustration of a typical AI answer; verdicts reflect the cited authority in the Kingsfield corpus as of the ruling date shown above.