In the case of Union Labor Life Insurance Co. v. Pireno, 1981, the U.S Supreme Court ruled on whether an insurance company's use of a peer review committee to determine reasonable and necessary medical expenses constituted a violation under the Sherman Antitrust Act. The plaintiff, Dr. Pireno, claimed that this practice was anti-competitive as it allowed insurers to collectively decide which claims were valid or not without any competition or market forces at play. However, the court held that such practices did not constitute a "boycott" nor were they outside of normal business operations for an insurance company under federal antitrust laws because they are part of providing insurance services rather than being separate from them and thus fall within McCarran-Ferguson Act’s exemption for “the business of insurance.” Therefore, these practices could be regulated by state law but would not violate federal antitrust laws unless there was evidence showing intent to monopolize or restrain trade in violation with those laws.

In the dissenting opinion for Union Labor Life Insurance Co. v. Pireno, Justice Rehnquist disagreed with the majority's interpretation of McCarran-Ferguson Act and its application to this case. He argued that the New York statute in question was enacted for regulating insurance business within state boundaries, thus it should be exempted from federal antitrust laws under McCarran-Ferguson Act. The justice also contended that chiropractic services are a part of health care industry rather than insurance industry; therefore, their peer review process does not constitute "the business of insurance". Furthermore, he criticized the majority’s reliance on three criteria set forth in another case (SEC v National Securities) as they were not designed to interpret “business of insurance” clause but rather an entirely different provision in a different act. Lastly, he expressed concern over potential negative impacts on states’ ability to regulate their own industries due to broad interpretation by federal courts.