Justice Powell argued that the Court discarded National League of Cities too abruptly and without the special justification required to overrule a recent constitutional precedent repeatedly reaffirmed by the Court. In his view, the majority disregarded stare decisis even though the Court had continued to apply National League of Cities in cases decided only a few years earlier.
He contended that the majority mischaracterized National League of Cities as requiring courts to classify functions through a rigid historical formula. Properly understood, that case and its successors used a balancing approach: courts should weigh the strength of the federal interest, including its connection to interstate commerce, against the degree to which federal regulation impairs a state's ability to perform core governmental functions.
Powell rejected the majority's reliance on political safeguards. Federal legislators serve the National Government once elected, and the President is not a representative of state interests merely because states participate in presidential elections. Political success in securing funds or statutory exemptions also does not answer whether Congress has exceeded a constitutional limit. In his view, the states' constitutional status cannot depend on federal legislative grace.
He maintained that the Tenth Amendment and the constitutional history of ratification confirm that states retain a judicially enforceable sphere of sovereignty. Judicial review is necessary when Congress regulates states as states; otherwise Congress becomes the sole judge of the limits of its own commerce power.
Applying that framework, Powell concluded that a municipally operated urban transit system is a classic local public service, closely akin to streets, lighting, water, sanitation, and traffic control. Federal control over state and local employees' wages, hours, pensions, and labor relations could substantially disrupt local budgeting, taxation, and the delivery of public services. Because the state interest was compelling and the majority identified no demonstrably stronger federal interest, he would have affirmed the judgment for SAMTA.