In Ad Investment 2000 Fund LLC v. Commissioner, 142 T.C. No. 13 (2014), the U.S. Tax Court held that a taxpayer’s assertion of a “reasonable belief” defense waived the attorney-client privilege. In this case, petitioner taxpayer asserted as a defense to “accuracy related” penalties that he reasonably believed that his tax treatment of partnership items was more likely than not the proper tax treatment at the time of filing. The tax regulations provide two methods for establishing this belief: (1) a “self-determination” method, based on the analysis of facts and authorities at the time of filing; and (2) reliance on the opinion of a professional tax advisor. It was undisputed that petitioner raised only a “self-determination” defense, and clearly stated that he did not intend to rely on the advice of counsel as a defense in the case. The Commissioner sought discovery of any tax opinions reviewed by the petitioner on the grounds that those opinions were relevant to the “good faith” belief asserted by petitioner. Petitioner argued that the statute provides two different methods for proving reasonable belief: one that would waive the privilege and one that would not. The court agreed with the Commissioner, holding that, by putting his “reasonable belief” at issue, petitioner waived privilege over any tax opinions that he received before taking the questioned positions and “presumably before making his alleged self-determination of authorities”.