31 CFR § 10.2 – Definitions.
(a) As used in this part, except where the text provides otherwise –
(1) Attorney means any person who is a member in good standing of the bar of the highest court of any state, territory, or possession of the United States, including a Commonwealth, or the District of Columbia.
Peter, the Tax Court is an Article 1 court, and I don’t believe it would qualify as a highest court in any of those descriptions. You can check further if you want more clarification from Federal Claims court, but that is beyond the scope of this exam and wouldn’t be tested for this purpose.