This sounds like a CP2000 notice. It usually means that there was an income item (usually reported on a W-2 or form 1099) that was not included on your return.

To respond to this letter, you need to do the following:

From IRS Understanding Your IRS CP2000:

What you need to do

• Read your notice carefully—it explains the information we received and how it affects your tax return.

• Complete the notice response form whether or not you agree or disagree with the notice, the response form explains what actions to take. (Your specific notice may not have a response form. In that case, the notice will have instructions on what to do).

• Contact the business or person reporting the information, if it is wrong. Ask them to correct it, and then provide the corrected information to us.

• Make sure your other returns don’t have the same mistake.

• Contact us with any unanswered questions you have.

• Keep a copy of the notice for your files.

• Fill out section 3 (Authorization) on the response form to allow someone, in addition to yourself, to contact us concerning this notice. Or send us a Form 2848, Power of Attorney and Declaration of Representative to allow someone (such as an accountant) to contact us on your behalf.

• Correct the copy of your tax return that you kept for your records.

• Order a transcript of your return.

• Use this link to learn more about your payment options if you owe additional taxes.

• Use this link to learn more about payment plans and installment agreements if you can’t pay the full...

• Use this link to learn more about Offers in Compromise if you can’t pay the full amount of taxes you...