Steve R. Johnson (UNLV) has published An IRS Duty of Consistency: The Failure of Common Law Making and a Proposed Legislative Solution , 77 Tenn L. Rev. (2010).  Here is the abstract:

The IRS should endeavor to treat similarly situated taxpayers similarly. But does this aspiration rise to the level of a judicially enforceable duty? If the IRS takes a position as to Taxpayer B which is correct under the law but is inconsistent with a position the IRS took as to similarly situated Taxpayer A, should the IRS lose as to Taxpayer B simply because of the inconsistency? These questions implicate important themes, such as fairness, the rule of law, separation of powers, administrative exigencies, the role of common law making in a highly positivistic system, and the sustainability of legal regimes.