From www.irs.gov:   IRS Summertime Tax Tip 2013-22
Each year the IRS sends millions of letters and notices to taxpayers. Although some people may feel anxious when they receive one, many are easy to resolve. Here’s what to do if you receive a letter or notice from the IRS:
1. Don’t panic. Follow the instructions in the letter.
2. There are many reasons the IRS sends notices to taxpayers. The notice usually covers a specific issue about your account or tax     return. It may request payment of taxes, notify you of a change …