Only the largest firms can violate the antitrust laws through unilateral conduct, that is conduct that does not involve an agreement with another firm. To do so, a firm must have monopoly power or a dangerous probability of obtaining it. Courts define this level of power as the ability to raise price or exclude competition from the market. In general, a firm must have at least a 50% market share, and often much more, before a court will find that it possesses monopoly power.
If a firm has monopoly power, a court will examine a challenged business practice to determine whether that practice harms consumers of the product or service in question by raising price, lowering quality, or retarding innovation.
Unilateral conduct cases generally come in two forms. Monopolization cases involve a company with monopoly power employing a business practice to maintain or expand its market position by hindering the ability of small competitors or potential competitors to gain market share. A recent example is the Microsoft case in which the company was found to have monopolized the market for PC operating systems by discouraging computer manufacturers from installing competing web browsers to Microsoft’s Internet Explorer.
The second form of unilateral conduct case involves an attempt to monopolize. In such a case, a firm that currently does not have monopoly power, but that is dangerously close to obtaining it, can be guilt of attempting to monopolize the market by employing a business practice to maintain or expand its market position by hindering the ability of small competitors or potential competitors to gain market share.