CP2100 Notice: What It Is and
How to Respond Step by Step

What Is a CP2100 Notice?

A CP2100 notice is an official IRS communication sent to payers (businesses that file information returns) informing them that one or more name/TIN combinations on their 1099 filings did not match IRS records. The notice lists every payee account with a discrepancy and instructs the payer to take corrective action.

The IRS sends two versions of this notice:

• CP2100 -- Sent to payers with a large number of mismatches. The notice typically includes a listing on electronic media (CD or downloadable file) rather than a paper list.
• CP2100A -- Sent to payers with a smaller number of mismatches. The payee listing is included directly in the paper notice.

Both versions carry the same legal weight and the same response requirements. The only difference is the format of the payee listing. Whether you receive a CP2100 or CP2100A, your obligations are identical.

Why Does the IRS Send CP2100 Notices?

The IRS requires accurate TINs on every information return to match reported income to the correct taxpayer. When the name and TIN on a 1099 do not match the IRS master file, the agency cannot properly credit that income. The CP2100 notice is the IRS's mechanism for pushing the correction burden back to the payer.

Common reasons a name/TIN combination triggers a CP2100 include:

• Data entry errors -- A transposed or missing digit in the TIN is the most common cause. Even a single wrong digit means the return will not match.
• Name discrepancies -- The legal name on your 1099 does not match the name the IRS or SSA has on file. This often happens when a vendor uses a DBA name instead of their legal name.
• Name changes -- A payee changed their legal name (through marriage, divorce, or corporate restructuring) but did not update their W-9.
• Wrong TIN type -- Using an EIN when the payee's IRS record is under an SSN, or vice versa. The IRS result codes can help you identify these mismatches.
• Stale records -- Vendor information that was correct when originally collected has become outdated over time.

Understanding what happens when a TIN doesn't match helps you appreciate why the IRS takes this seriously: unmatched income creates a gap in the tax system that the agency is legally required to close.

CP2100 Response Timeline: Key Dates

The moment you open a CP2100 notice, the clock starts. Here are the critical deadlines:

These deadlines are strict. The IRS expects you to act within 15 business days of the notice date -- not 15 business days from when you opened the envelope. Organizations with strong vendor compliance processes designate a specific person or team to receive and act on IRS notices immediately.

Step-by-Step: How to Respond to a CP2100 Notice

Step 1: Review the Payee Listing

Open the CP2100 and review every name/TIN combination flagged by the IRS. Compare each entry against your current vendor records. In some cases, you may find that you already have corrected information on file -- perhaps a vendor submitted an updated W-9 after the filing in question. For those accounts, verify the corrected information using IRS TIN matching and document that the issue has been resolved.

Step 2: Attempt to Verify Internally

Before sending B-Notices, run the flagged TINs through bulk TIN matching. Some mismatches may have resulted from data entry errors on your filing -- for example, you may have transposed a digit when entering the TIN on the 1099, even though your vendor master file has the correct number. If the TIN in your records matches the IRS, the problem was in the filing, not the vendor data. Document this finding and review the result codes for each verification.

Step 3: Send First B-Notices

For every payee whose TIN you cannot independently verify, you must send a First B-Notice. IRS Publication 1281 provides the required language for this notice. The First B-Notice must include:

• A statement that the IRS has notified you that the payee's name/TIN combination does not match
• A request that the payee provide their correct name and TIN
• A blank Form W-9 for the payee to complete and return
• A statement that you must begin backup withholding if the payee does not respond within 30 days

You must mail First B-Notices within 15 business days of the CP2100 notice date. Keep copies of every notice sent and record the mailing dates.

Step 4: Process Payee Responses

As payees return completed W-9 forms, verify each new name/TIN combination through TIN matching immediately. Do not simply accept the W-9 at face value -- a payee may return a form with the same incorrect information, or with new errors. Real-time verification confirms that the corrected information actually matches the IRS database.

Update your vendor master file with verified information and flag the account as resolved. This documentation is critical for establishing reasonable cause if the IRS questions your compliance efforts.

Step 5: Begin Backup Withholding for Non-Responders

If a payee does not respond within 30 calendar days of your B-Notice, you are legally required to begin backup withholding at 24% on all reportable payments to that payee. This is not optional. The IRS holds payers liable for the withheld amount whether or not you actually withhold it from the payee's payments.

Report backup withholding on Form 945 (Annual Return of Withheld Federal Income Tax) and provide each affected payee with a corrected 1099 showing the withholding amount.

Step 6: Document Your Entire Response

Maintain a complete record of your response to the CP2100 notice. This should include:

• The original CP2100 notice and payee listing
• Results of your internal TIN verification efforts
• Copies of all B-Notices sent, with mailing dates
• Payee responses received, with dates
• TIN matching results for corrected information
• Backup withholding start dates for non-responsive payees

This documentation is your defense against IRS penalties. Under IRC Section 6724, you can avoid penalties by demonstrating that you acted with reasonable cause and not willful neglect. A well-documented response to a CP2100 notice is strong evidence of due diligence.

What Happens If You Ignore a CP2100 Notice?

Ignoring a CP2100 notice does not make it go away. The consequences escalate:

• Backup withholding liability -- You owe the IRS 24% of all reportable payments made to the mismatched payees from the date withholding should have started, regardless of whether you actually withheld. See our backup withholding guide for details.
• Per-return penalties -- The IRS can assess penalties up to $680 per incorrect return with no annual cap for intentional disregard.
• Second B-Notice escalation -- If the same payees appear on a subsequent CP2100, the Second B-Notice rules are far more restrictive. The payee can no longer simply submit a new W-9 -- they must get direct IRS or SSA validation.
• Loss of reasonable cause defense -- Failing to respond to a known notice eliminates your ability to claim reasonable cause for the incorrect filing.

CP2100 vs. CP2100A: Is There a Difference?

The only practical difference between a CP2100 and CP2100A is the format of the payee listing. A CP2100 is sent when you have a larger number of mismatches, and the payee list is typically provided on electronic media. A CP2100A is sent for smaller volumes, with the payee list printed directly on the notice. The IRS's own CP2100 notice page confirms that the response requirements are identical for both versions.

Some organizations receive a CP2100 one year and a CP2100A the next, depending on how many mismatches the IRS found. The notice version does not change your obligations.

How TIN Matching Prevents CP2100 Notices

The entire CP2100 process exists because payers filed 1099s with incorrect TINs. The most straightforward way to prevent CP2100 notices is to verify every name/TIN combination before you file. The IRS's TIN Matching Program exists for exactly this purpose.

TINCorrect connects to the IRS TIN Matching Program and lets you verify TINs at scale -- whether you need to check a single vendor or tens of thousands at once. Here is how it fits into your 1099 compliance workflow:

Organizations that verify TINs before filing typically see their CP2100 notice volume drop dramatically -- often to zero. When every TIN on your 1099s matches the IRS database, there are no mismatches for the IRS to flag. No mismatches means no CP2100, no B-Notices, no backup withholding, and no penalties.

Responding to a CP2100 After Already Implementing TIN Matching

If you already use TIN matching and still receive a CP2100, it usually means one of two things: the mismatch occurred on returns filed before you started verifying, or the vendor's information changed after your last verification. In either case, your response process is the same -- but your documentation will be stronger because you can show the IRS your established verification program.

Going forward, consider adding a second verification pass immediately before filing. Run bulk TIN matching against your entire 1099 population in December or early January, even if you verified during vendor onboarding. This catches any changes that occurred between onboarding and filing season.

Frequently Asked Questions

Author

Ken Ham

Founder at TINCorrect

Passionate about making tax identity verification simple so businesses can focus on what matters.