Who knows best, the I.R.S. or the U.S. Supreme Court? Refusing to give up on its position that Code §482 trumps a foreign law that caps amounts used in related-party transactions, the I.R.S. is challenging 3M, a corporation that is acting in compliance with Brazilian law. Elizabeth V. Zanet and Galia Antebi delve into a legal issue that most adviser though was settled years ago by the U.S. Supreme Court.