When you have a dispute with the IRS, you’ll need to show that the law supports what you did if you want to win your argument. Support directly from the Internal Revenue Code is the best proof. You can also use Treasury Department or other IRS interpretations of the Internal Revenue Code to support your position, such as Treasury Regulations, Revenue Rulings or Revenue Procedures, and Announcements and Notices.
We strive to find your deductions in one of the sources above. A private letter ruling, while not authority unless you requested it for your situation, can prove useful to us because it shows the IRS reasoning on a specific situation.
What’s interesting is that you can’t rely on IRS form instructions, IRS publications, the IRS website, or the Internal Revenue Manual. These are not authority according to both the IRS and the courts. We use them to help us find that higher authority that we can then apply to your situation.