The United States Tax Court is a specialized court that only hears and adjudicates federal tax matters. It is made up of a panel of 19 judges who are tax experts. There are no juries in Tax Court.
If the IRS is proposing to adjust the amount of tax you owe, you will typically be sent a “Notice of Deficiency,” also referred to as a “90-Day Letter,” which informs you of the proposed change. Once the notice has been issued, you have 90 days from the date on that notice to file a petition with the Tax Court in order to challenge the proposed adjustment without first having to pay the proposed adjustment. (The deadline is extended to 150 days if the taxpayer is out of the country at the time the notice is mailed.)
If you miss the 90-day deadline, the statute of limitations has expired and you must pay the tax. You may still have your case heard in U.S. District Court. However, to get into District Court, you must first pay the tax liability and then file a claim for a refund.