In the case of Leroy, Attorney General of Idaho, et al. v. Great Western United Corp., 1978, the U.S Supreme Court ruled in favor of Great Western United Corporation (GWUC). The dispute arose when Idaho passed a law that prevented GWUC from purchasing more than 10% of its own sugar beet crop for two years. This was done to protect local farmers and maintain competition within the industry. However, GWUC argued this violated their rights under both Commerce Clause and Equal Protection Clause as it interfered with interstate commerce and discriminated against out-of-state businesses respectively. The court held that while states have power to regulate commerce within their borders, they cannot enact laws which discriminate against or excessively burden interstate commerce unless there is no other means to achieve an important state interest. In this case however, it found that Idaho's law did not serve any legitimate state purpose but rather imposed onerous restrictions on out-of-state companies like GWUC thereby violating both clauses mentioned above.

In the dissenting opinion for Leroy v. Great Western United Corp., Justice Rehnquist disagreed with the majority's decision to allow a corporation to seek damages under federal antitrust laws due to state action that allegedly caused it harm. He argued that this interpretation of the Sherman Act was too broad and not in line with its original intent, which was primarily aimed at private commercial restraints on trade rather than actions by states or their officials. Furthermore, he contended that allowing such claims could potentially open up a floodgate of litigation against states and their officials for carrying out their duties, thus undermining state sovereignty. He also pointed out inconsistencies in how the court had previously interpreted similar cases involving alleged violations of federal antitrust laws by states or public entities.