If you received Letter 531 Notice of Deficiency from the IRS, please see the following information from IRS Letters and Notices Offering an Appeal:
This letter is notice of the Commissioner's determination that you owe additional tax or other amounts for the tax year(s) identified in the letter. The Internal Revenue Code authorizes the Commissioner to send this notice. The letter explains how to dispute the adjustments in the notice of deficiency if you do not agree. To dispute the adjustments without payment, you must file a petition with the Tax Court within 90 days from the notice date.