By Andrew Roberson and Timothy Shuman (January 7, 2019, 3:50 PM EST) -- The Supreme Court's recent decision to grant certiorari in the case of James L. Kisor v. Peter O'Rourke, Acting Secretary of Veteran Affairs, and revisit the question of whether an administrative agency's interpretation of its own ambiguous regulations is entitled to deference, could have a cascading effect on deference principles in general. In the tax arena, this development has wide-ranging implications for tax planning and litigation matters going forward. Although taxpayers and tax professionals have wrestled with deference issues for years, this development takes on added importance given the major recent changes to the tax laws and Treasury's tremendous effort to draft thousands of pages of regulations in response....