MeadWestvaco Corp. v. Illinois Department of Revenue

The Due Process and Commerce Clauses forbid the States to tax “‘extraterritorial values.’” Container Corp. of America v. Franchise Tax Bd., 463 U. S. 159,164 (1983); see also Allied-Signal, Inc. v. Director, Div. of Taxation, 504 U. S. 768, 777 (1992); Mobil Oil Corp. v. Commissioner of Taxes of Vt, 445 U. S. 425, 441-442 (1980). A State may, however, tax an apportioned share of the value generated by the intrastate and extrastate activities of a multistate enterprise if those activities form part of a “‘unitary business.’” Hunt-Wesson, Inc. v. Franchise Tax Bd. of Cal., 528 U. S. 458, 460…