Many of these letters can be dealt with simply, without having to call or visit an IRS office. For example, you may get a letter that states the IRS made a change or correction to your tax return. If you do receive this letter, review the information and compare it with your original return. If you agree, you usually don’t need to reply unless it gives you other instructions or you need to make a payment.

However, if you don’t agree with the letter, it’s important for you to respond. Write to explain why you disagree and include any information and documents you want the IRS to consider. If you have questions, call the telephone number in the letter. We can help you prepare responses and talk to the IRS on your behalf. Typical notices relate to

-late filing penalties

-Broker account issues 

-missed 1099's 

-tax returns being filed by the IRS for prior non-filed years 

https://www.irs.gov/individuals/understanding-your-irs-notice-or-letter