Three years ago, the U.S. Supreme Court invalidated a portion of Maryland’s personal income tax scheme on grounds that it violated the dormant commerce clause of the U.S. Constitution. In Comptroller of the Treasury of Maryland v Wynne, the Court held that Maryland’s credit mechanism for income taxes paid to other states impermissibly discriminated against interstate commerce because it allowed a credit against state taxes paid but not county taxes, resulting in double taxation on some income earned outside the state.