Congress and the Internal Revenue Service continue to view tax shelters with a high level of scrutiny, with Congress enacting legislation and the IRS promulgating rules designed to limit the ability of taxpayers to take certain tax positions. One of the weapons in the IRS's arsenal is its ability to identify certain transactions as "listed transactions." This article addresses the IRS notice, as well as the recent US district court decision in Enbridge Energy Co v. US, which deals with the tax strategy the IRS notice attempts to thwart. The ambiguous wording of Notice 2008-20 make it hard to determine whether certain transactions will be covered by the Notice, and indeed, its broad scope raises a serious risk of inadvertent participation in a tax shelter for both sellers and buyers. The potential penalties involved here are severe. Failure to disclose a listed transaction, or a substantially similar transaction, on a return or statement will result in a penalty of $200,000.