A line of cases from the U.S. Supreme Court has long held that ownership of a patent is presumed to convey market power, which is one of the factors needed to prove that an illegal tying arrangement exists in contravention of Section 1 of the Sherman Act.
Market power indicative of illegal tying is appreciable economic power in the market for the tying product affecting a substantial volume of commerce in the tied market [Eastman Kodak Co. v. Image Technical Services, 504 U.S. 451, 462 (1992)].
For tying to be illegal the seller must be able to appreciably restrain free competition in the market for the tied product [United States v. Loews, Inc., 371 U.S. 38, 45 (1962)].
If no patent is involved, then market power is proved by showing that the seller is able to raise prices or require purchasers to accept burdensome terms that could not be exacted in a completely competitive market [United States Steel Corp. v. Fortner Enterprises, Inc., 429 U.S. 610, 620 (1977)].
However, if a patent covers the tying product, then market power is presumed [International Salt Co. v. United States, 332 U.S. 392 (1947)].
The doctrine linking patent ownership with market power has been subject to frequent criticism. While a patent provides a monopoly over the claimed invention for the term of the patent, there are several arguments suggesting that the patent monopoly does not automatically result in market power.
For example, there may be alternative technologies on the market, and the patented invention might exclude competition from only a limited market share. Or, it might be fairly easy to design around the patent to develop alternatives. After all, theres more than one way to build a mousetrap.
The presumption of market power based on a patent has fallen into disfavor in recent years, and some courts have declined to follow it. As a matter of policy, the Department of Justice, which enforces the antitrust laws, does not presume that market power exists based merely on patent ownership, and states so in its Antitrust Guidelines for the Licensing of Intellectual Property.