On May 18, the U.S. Supreme Court issued its decision in Comptroller of the Treasury of Maryland v. Wynne. In short, the Court, in a five-to-four decision written by Justice Alito, handed the taxpayer a victory by holding that the county income tax portion of Maryland’s personal income tax scheme violated the dormant U.S. Constitution’s Commerce Clause.

Specifically, the Court concluded that the county income tax imposed under Maryland law failed the internal consistency test under the dormant Commerce Clause, because it is imposed on both residents and non-residents with Maryland residents not getting a credit against that Maryland local tax for income taxes paid to other jurisdictions (residents are given a credit against the Maryland state income tax for taxes paid to other jurisdictions).

The Supreme Court emphatically held (as emphatically as the Court can be in a five-to-four decision) that the dormant Commerce Clause’s internal consistency test applies to individual income taxes. The Court’s holding does create a perilous situation for any state or local income taxes that either do not provide a credit for taxes paid to other jurisdictions or limit the scope of such a credit in some way.

The internal consistency test—one of the methods used by the Supreme Court to examine whether a state tax imposition discriminates against interstate commerce in violation of the dormant Commerce Clause—starts by assuming that every state has the same tax structure as the state with the tax at issue. If that hypothetical scenario places interstate commerce at a disadvantage compared to intrastate commerce by imposing a risk of multiple taxation, then the tax fails the internal consistency test and is unconstitutional.

Although the Wynne decision does not address the validity of other taxes beyond the Maryland county personal income tax, the decision does create significant doubt as to the validity of certain other state and local taxes such as the New York State personal income tax in the way it defines “resident.” New York State imposes its income tax on residents on all of their income and on non-residents on their income earned in the state; this is similar to the Maryland county income tax at issue in Wynne.

“Resident” is defined as either a domiciliary of New York or a person who is not a domiciliary of New York but has a permanent place of abode in New York and spends more than 183 days in New York during the tax year. N.Y. Tax Law § 605. (New York City has a comparable definition of resident.) N.Y.C. Administrative Code § 11-1705. Thus a person may be taxed as a statutory resident solely because they maintain living quarters in the state and spend more than 183 days in the state, even if those days have absolutely nothing to do with the living quarters; this category of non-domiciliary resident is commonly referred to a “statutory resident.” As such, under New York’s tax scheme, a person can be a resident of two states—where domiciled and where a statutory resident—and thus [...]

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