In competition law, a group boycott is a type of secondary boycott in which two or more competitors in a relevant market refuse to conduct business with a firm unless the firm agrees to cease doing business with an actual or potential competitor of the firms conducting the boycott.^[1] It is a form of refusal to deal, and can be a method of shutting a competitor out of a market, or preventing entry of a new firm into a market.

In the United States, such conduct can be held to violate the Sherman Antitrust Act. Depending upon the nature of the boycott, the courts may apply the rule of reason, a quick look analysis, or hold that the boycott is illegal per se. There is a presumption in favor of a rule of reason standard.^[2][3] It may also be considered a form of civil conspiracy.

• Freedom of association
• Refusal to deal
• Primary boycott
• Secondary boycott