Martin J. McMahon, Jr. (Florida) & Ira B. Shepard (Houston) have published Privilege and the Work Product Doctrine in Tax Cases, 58 Tax Law. 405 (2005).  Here is the abstract:

Over the past few years, the applicability of the attorney-client privilege, the related section 7525 tax practitioner-client privilege, and the work product doctrine have emerged as significant issues in tax litigation. For the most part, the recent cases have arisen in the context of marketed tax shelters and other aggressive tax planning transactions, but a few of the cases have surfaced in more prosaic contexts. As a result of the recent firestorm of controversy in this area, tax practitioners are becoming increasingly conscious of the importance of raising privilege and work product doctrine challenges when the Service seeks information about taxpayers’ transactions pursuant to a summons or in the course of discovery. This article is intended to acquaint practitioners with the core principles governing resolution of controversies of this nature.