Copperweld Corp. v. Independence Tube Corp.

In Copperweld Corp. v. Independence Tube Corp., 467 U.S. 752, 777 (1984), the U.S. Supreme Court held that a parent cannot combine with its wholly-owned subsidiary for purposes of section 1 of the Sherman Act. Likewise, an employee generally cannot conspire with his employer for the purposes of the Sherman Act.

But there is an exception to this rule when an individual has his own financial interest in the conspiracy that is separate from that of the principal, and if the individual could coerce the principal to impose the restraint of trade.

Also in this decision the Court equated the rule of reason with "an inquiry into market power and market structure designed to assess [a restraint's] actual effect." Id. at 768.