Receive a summons
If the IRS is having trouble sorting out the taxes you owe, you could get a summons — that's a legal requirement to appear — to meet with an IRS officer, and bring appropriate records, documents, and possibly even testify.
It won't necessarily be you who is asked to meet with the agency: A third party with information relevant to your case, such as a record keeper from a financial institution, could be summoned instead. If the IRS is simply gathering info, you'll be informed of the third-party summons, but if it's in reference to money it's already clear you owe, you might not even find out.