Empagran S.A. and other foreign and domestic companies that purchased vitamins for distribution (plaintiffs) filed a class action against several foreign and domestic vitamin sellers, including F. Hoffmann-La Roche, Ltd. (defendants). The vitamin purchasers alleged the vitamin sellers engaged in a price-fixing conspiracy. The vitamin sellers moved to dismiss the foreign purchasers’ claims, arguing these claims were based on foreign conduct that is outside the reach of domestic antitrust laws. The district court agreed and dismissed the foreign purchasers’ claims. The domestic purchasers pursued their claims in a separate suit. The court of appeals reversed the dismissal of the foreign purchasers. The court of appeals found that, even if the conduct at issue in the foreign purchasers’ claims only affected prices in foreign countries, the conduct was part of a conspiracy that, as a whole, had a direct and substantial effect on domestic commerce. The vitamin sellers filed a petition for certiorari with the United States Supreme Court.