Western & Southern Life Insurance Co. v. State Board of Equalization of California

California imposed a retaliatory tax on out-of-state insurers whose home states taxed California insurers more heavily than California would otherwise tax in-state business; Western & Southern (plaintiff), an out-of-state insurer subject to the tax, sued the state tax board (defendant) claiming the tax unconstitutionally burdened interstate commerce. The state appellate court upheld the tax after the trial court had struck it down, and Western & Southern appealed to the Supreme Court.

Whether a state may impose a retaliatory tax on out-of-state businesses that would otherwise violate the dormant Commerce Clause when Congress has authorized such state regulation.