A national bank chartered under the National Bank Act is treated as a citizen of the state in which it is "located." In 2006, the Supreme Court rejected an approach that would have interpreted the term "located" to mean that a national bank is a citizen of every state in which it maintains a branch. The Supreme Court concluded that “a national bank . . . is a citizen of the State in which its main office, as set forth in its articles of association, is located.” The Supreme Court, however, left open the possibility that a national bank may "also" be a citizen of the state in which it has its principal place of business, thus putting it on an equal footing with a state-formed corporation. This remains an open question, with some lower courts holding that a national bank is a citizen of "only" the state in which its main office is located, and others holding that a national bank is "also" a citizen of the state in which it has its principal place of business.