On May 18, the United States Supreme Court held that Maryland’s state income tax could not be applied to out of state income sources.  The Court’s opinion appeared to adopt and clarify the doctrine that only one state can be permitted to tax the same income.  I copy of the SCOTUS opinion can be found here.

Although the State House is seeking to impose an income tax on Washington residents who recognize capital gains, Washington does not currently have an individual income tax.  Assuming that the State Senate continues to block the state income tax effort, however, the Supreme Court’s ruling has significance for the state’s Business & Occupation Tax, which is imposed on business gross receipts.  It is possible, although not by any means certain, that the Department of Revenue will review or consider new regulations in light of the Court’s ruling.

The Court’s opinion was authored by Justice Alito; Justices Roberts, Kennedy, Breyer and Sotomayor joined.