joint refusal to deal resulting in an exclusion of traders from the competitive market is a per se violation of section 1 of the Sherman Act.
United States v. General Motors Corp., 384 U.S. 127 (1966).
David J. Pleva,
Trade Regulations - Group Boycott - Restraint of Trade,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol5/iss2/14