Hunt-Wesson, Inc. v. Franchise Tax Board of California

A State may tax a proportionate share of the income of a nondomiciliary corporation that carries out a particular business both inside and outside that State. Allied-Signal, Inc. v. Director, Div. of Taxation, 504 U. S. 768, 772 (1992). The State, however, may not tax income received by a corporation from an “ ‘ “unrelated business activity” ’ which constitutes a ‘“discrete business enterprise.”’” Id., at 773 (quoting Exxon Corp. v. Department of Revenue of Wis., 447 U. S. 207, 224 (1980), in turn quoting Mobil Oil Corp. v. Commissioner of Taxes of Vt., 445 U. S. 425, 442, 439 (1980)).…