In a 5-4 decision in Comptroller v. Wynne the Supreme Court held that Maryland’s failure to offer residents a full credit against income taxes paid to other states is unconstitutional. The State and Local Legal Center (SLLC)/International Municipal Lawyers Association (IMLA) filed an amicus brief in support of Maryland.
Maryland taxes residents’ income earned in- and out-of-state. If Maryland residents pay income tax to another state for income earned there, Maryland allows them a credit against Maryland’s “state” tax but not its “county” tax. Maryland also taxes nonresident income earned in the state. Nonresidents pay Maryland “state” tax and a “special nonresident tax” equivalent to Maryland’s lowest “county” tax.