JUSTICE O'CONNOR, concurring in part and concurring in the judgment.
I agree that the Illinois Telecommunications Excise Tax Act does not violate the Commerce Clause, and join Parts I, II-A, II-D, and III of the Court's opinion. I write separately to explain why I do not join Parts II-B and II-C. First, I am still unsure of the need and authority for applying the internal consistency test to state taxes challenged under the Commerce Clause. See American Trucking Assns., Inc. v. Scheiner, 483 U. S. 266, 483 U. S. 303 (1987) (O'CONNOR, J., dissenting). I therefore do not join in the Court's application of that test to the Tax Act. Ante at 488 U. S. 261. Second, I agree with JUSTICE STEVENS that a State may not discriminate among its own residents by placing a heavier tax on those who engage in interstate commerce than those who merely engage in local commerce. Ante at 488 U. S. 268 (STEVENS, J., concurring in part and concurring in judgment). Accordingly, I cannot join the Court's statement that "[i]t is not a purpose of the Commerce Clause to protect state residents from their own state taxes." Ante at 488 U. S. 266.