IRS Letter 566 initiates a correspondence audit, requiring taxpayers to substantiate specific return items by mail. The notice identifies the tax year and documentation requested, such as receipts, W-2s, 1099s, K-1s, or proof of deductions and credits. Inadequate responses can result in additional tax, penalties, interest, or expanded review. Ayar Law represents Michigan taxpayers in IRS audits, documentation responses, and appeals before the IRS Independent Office of Appeals.
IRS correspondence audit Letter 566 is the notice the IRS sends when it opens an audit that will be handled entirely by mail. Letter 566 zeroes in on one or a few line items on your tax return and asks you to send documentation proving those numbers are accurate. The IRS isn’t accusing you of fraud. It’s asking you to substantiate what you claimed.
A Letter 566 IRS notice is different from the automated balance-due letters that follow simple math errors or missing W-2s. This is a formal examination. The IRS has identified specific items it wants to verify, and your response directly affects the outcome. If you can’t prove the item, the IRS will disallow it, propose additional tax, and tack on penalties and interest dating back to the original due date.
For taxpayers who claimed large business expenses, pass-through income from partnerships or S corporations, complex deductions, or refundable credits, the stakes are higher. A sloppy or incomplete response can expand the audit scope, pulling in additional tax years or related issues that weren’t originally in question.
Most correspondence audit cases include an IRS documentation request that lists the tax year under review, the specific line items being questioned, and the types of records the IRS will accept as proof. The letter might request:
Education credits, child-related credits, and home office deductions are also common targets. The IRS has specific standards for acceptable proof that are often stricter than expected. A credit card statement showing a charge to a charity, for example, is not sufficient on its own. You need a written acknowledgment from the charity that includes the date, amount, and a statement that no goods or services were provided in exchange for the donation.
The IRS expects copies (not originals) of your supporting documents with a brief written explanation connecting each record to your return. If your response is incomplete, inconsistent, or confusing, the IRS may disallow items even if you have the records. Organization and clarity can determine whether you get a favorable outcome or an unexpected bill.
Start by reading the letter carefully. Identify the exact items and tax year(s) under examination. Many taxpayers make the mistake of sending a shoebox full of “everything” in hopes that something will satisfy the IRS. That approach backfires. A targeted, organized response aligned to what the IRS audit letter actually requests is far more effective.
Cover letter: Include your name, taxpayer identification number, the tax year, and the letter ID (usually at the bottom right corner of the notice, such as “Letter 566-S”).
Document index: Create a list of each document by category and page number.
Labeled exhibits: Match the IRS’s requested categories. For example, Schedule A charitable contributions on pages 1-5, Schedule C business expenses on pages 6-12, and so on.
Clear presentation: Highlight totals and show calculations.
The IRS provides detailed guidance on organizing files for correspondence exams that can help you structure your response effectively.
Keep a complete copy of everything you mail. Use a trackable mailing method like certified mail with a return receipt. Meet the deadline listed on the notice. Missing it can result in the IRS making adjustments without your input, and those adjustments are rarely in your favor.
Before you mail anything, have a tax attorney review your Letter 566 response package. Missing documentation, unclear explanations, or accidental disclosures can expand the scope of the audit or trigger penalties. Call Ayar Law at (248) 262-3400 for a review before you send your response, and ideally before you prepare one. For more on preparing documentation, see How to Prepare for an IRS Audit.
Risks to Watch: Expanded Issues, Penalties, and Follow-Up Notices
If the IRS doesn’t accept your documentation, it will propose additional tax, assess penalties, and charge interest that accrues from the original due date. That interest compounds, and the bill grows quickly.
An IRS audit letter response can increase risk by accidentally raising new questions. Documents that don’t match the return, inconsistent explanations, or incomplete records can prompt the auditor to expand the examination. For business owners and higher-income taxpayers, this can lead to broader scrutiny of income sources, related deductions, and even other tax years. What started as a question about one Schedule C deduction can become a full examination of your entire business operation.
If the IRS proposes changes to your tax return(s), you have options. You can agree with the proposed changes, provide additional documentation, or disagree and request an appeal. Knowing when to escalate to the IRS Independent Office of Appeals is key, particularly when the dispute centers on substantiation, interpretation of tax law, or reasonable cause.
A tax attorney can interpret what Letter 566 is really asking for and identify gaps in your documentation that could trigger a denial. This includes ensuring your response matches IRS substantiation rules, not just what seems reasonable from a taxpayer perspective. The IRS has specific requirements, and meeting them often requires more than common sense.
A tax attorney can strategically organize your response, avoid disclosures that could expand the audit, and handle negotiations or appeals if needed. This is especially valuable for business expenses or complex deductions that require specific substantiation. Another benefit of working with a tax attorney is that the attorney-client privilege protects your discussions if the audit takes an unexpected turn.
Don’t face the IRS alone. Call Ayar Law at (248) 262-3400 to get a tax attorney’s help responding to the documentation request and protecting you from expanded audit issues, penalties, or collections. We’ve handled hundreds of IRS audits and can review your case, organize your response, and represent you through appeals if needed.
Contact us today for a confidential case review.
