In the 1984 case Southern Motor Carriers Rate Conference, Inc. v. United States, the Supreme Court ruled that state action immunity does not apply to federal antitrust laws unless it is clear that a state intended to displace competition in a particular field with its own regulatory process. The case involved rate bureaus which were comprised of interstate motor carriers operating within certain states and had been authorized by those states' legislatures to collectively set rates for their services. These activities were challenged under federal antitrust law but the defendants claimed they were immune due to being sanctioned by state legislation. However, the court found no explicit evidence of these states intending such an exemption from federal regulation and thus held that this 'state action immunity' did not protect them from liability under anti-trust laws.

In the dissenting opinion for Southern Motor Carriers Rate Conference, Inc. v. United States, Justice Powell argued that state action immunity should apply to the rate-making activities of interstate motor carriers because they were acting under clearly articulated and affirmatively expressed state policy to displace competition with regulation in this area. He contended that these actions were not only authorized but actively supervised by a regulatory body empowered by the State; thus satisfying both prongs of Midcal's two-part test for determining whether anticompetitive conduct is immune from federal antitrust laws under Parker doctrine (state-action immunity). Furthermore, he disagreed with majority’s view on active supervision requirement as it was never intended to be applied where private parties participate in a traditional area of state regulation such as transportation rates setting process which has historically been subject to extensive government control.