If you’ve received a CP2100 or CP2100A notice, correcting TIN mismatch errors comes down to a short sequence: match the flagged payees against your own records, send each one the right Backup Withholding Notice (a “B-Notice”), begin withholding 24% of their future reportable payments if they don’t respond in time, and stop withholding once they give you a valid Taxpayer Identification Number. Miss any of those steps and you become personally liable for the tax you should have collected, on top of per-return penalties that reach $340 in 2026.
What the CP2100 Notice Is Telling You
The IRS runs the name and TIN combinations from your filed information returns against its Master File and flags anything that doesn’t line up. A CP2100 goes to payers with 50 or more mismatched returns; a CP2100A goes to payers with fewer than 50. The content is identical.1Internal Revenue Service. Understanding Your CP2100 or CP2100A Notice
Each notice lists every payee whose name/TIN combination failed, along with codes identifying the specific problem: the TIN is missing, the TIN doesn’t match the name, or the TIN was never issued. Most mismatches trace back to ordinary things. A payee changed names after marriage without updating Social Security. A sole proprietor put a “doing business as” name on the W-9 instead of the owner’s personal name. A digit got transposed. A nickname replaced a legal name.
The notices arrive twice a year, in October and the following April.1Internal Revenue Service. Understanding Your CP2100 or CP2100A Notice Every deadline for responding runs from the date you received the notice, so a CP2100 sitting unopened in a mailroom is already eating into your response window.
Step 1: Compare the Payee List Against Your Records
Before contacting anyone, pull each flagged payee’s file and compare what’s on the 1099 to what your records actually show. If your files contain different (and correct) information than what was reported, the mistake was internal — a data entry error, an outdated name, a truncated TIN in your accounting software. You can fix those without ever writing to the payee.
When the error isn’t obvious from your own records, you need a corrected Form W-9 from the payee. For individuals, the name on the W-9 must match the Social Security card exactly. For sole proprietors, use the owner’s personal name, not the business trade name. And confirm the type of number matches the entity: SSN or ITIN for individuals, EIN for businesses. Mismatched number types are a common cause of repeat failures.2Internal Revenue Service. Instructions for the Requester of Form W-9
Step 2: Send the Correct B-Notice
You’re required to send a formal B-Notice to every payee on the CP2100 list. Which version depends on whether this is the payee’s first mismatch or a repeat.
First B-Notice
The first B-Notice tells the payee that their information didn’t match government records and asks them to return a completed, signed Form W-9. Include a blank W-9 and a return envelope.3Internal Revenue Service. Backup Withholding “B” Program
If the payee returns a corrected W-9 within 30 business days, update your records and no backup withholding is required. If they don’t respond in that window, you must begin withholding 24% from their future reportable payments no later than 30 business days after you received the CP2100.1Internal Revenue Service. Understanding Your CP2100 or CP2100A Notice
Second B-Notice
If the same payee appears on a CP2100 a second time within three calendar years, a new W-9 is no longer enough. Under the “two-in-three-years” rule, the payee must supply verification directly from the issuing agency:3Internal Revenue Service. Backup Withholding “B” Program
- Individuals with an SSN must provide a copy of their Social Security card.
- Businesses with an EIN must provide an IRS Letter 147C verifying the name and number on file.
The point of the escalation is verification from the issuing agency, not another self-certification. Keep a log of every B-Notice you send, with dates and delivery confirmation, so you can prove you followed the right process for the right payee if the IRS asks later.
Step 3: Start Backup Withholding If the Payee Doesn’t Respond
Backup withholding is a flat 24% taken from future reportable payments to any payee whose TIN problem remains unresolved.4Internal Revenue Service. Backup Withholding The obligation kicks in when the payee never provided a TIN, when the IRS notified you the TIN is incorrect, or when the payee fails to respond to your B-Notice on time.5Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding
Backup withholding covers most 1099-reportable payments, not just contractor pay. Nonemployee compensation on the 1099-NEC is the obvious one, but the rule also reaches rents and royalties on the 1099-MISC, interest on the 1099-INT, dividends on the 1099-DIV, broker and barter transactions on the 1099-B, third-party network payments on the 1099-K, and certain gambling winnings on the W-2G.6Internal Revenue Service. Topic No. 307, Backup Withholding If you pay a vendor rent for office space and that vendor’s TIN doesn’t match, you withhold from the rent payments too.
Tell affected payees before the first reduced check goes out. Many don’t realize their payments will be 24% short until the money arrives, and the amount can’t be refunded to them — they’ll claim it as a credit on their own income tax return for the year the income was received.4Internal Revenue Service. Backup Withholding
Step 4: Stop Withholding and File Corrections
Once a payee gives you a valid TIN, you must stop backup withholding no later than 30 calendar days after receiving the corrected information.1Internal Revenue Service. Understanding Your CP2100 or CP2100A Notice That deadline is calendar days, not business days. Update accounts payable or payroll immediately so withholding doesn’t continue past the cutoff.
You don’t send the corrected W-9 or B-Notice paperwork back to the IRS unless asked. The correction flows through your next scheduled information return filing: when you file the corrected 1099 with the right name/TIN, the IRS database is updated.
Amounts you already withheld have to be deposited through the Electronic Federal Tax Payment System (or IRS Direct Pay or your IRS business tax account) and reported on Form 945 at year-end.7Internal Revenue Service. Instructions for Form 945 Form 945 is due January 31 following the calendar year of withholding, extended to February 10 if every required deposit was on time and in full. File one Form 945 per year, regardless of how many payees were affected.
What Happens If You Don’t Withhold
If backup withholding was required and you didn’t do it, you owe the tax yourself. Federal law makes the payer personally liable for amounts that should have been deducted and withheld, and the IRS doesn’t treat that as a debt you can recover from the payee after the fact.5Office of the Law Revision Counsel. 26 USC 3406 – Backup Withholding That liability stacks on top of any information-return penalties.
The math is unforgiving. On a $100,000 annual vendor relationship where you should have been withholding but weren’t, that’s $24,000 out of your own pocket. This is what usually goes wrong: a business receives the CP2100, sets it aside, keeps paying full value, and discovers the exposure months later.
2026 Penalty Amounts for Incorrect Returns
Penalties under Section 6721 are tiered by how quickly you correct the error. For returns due in 2026:8Internal Revenue Service. Information Return Penalties
- Corrected within 30 days of the due date: $60 per return
- Corrected after 30 days but by August 1: $130 per return
- Corrected after August 1 or never filed: $340 per return
- Intentional disregard: $680 per return, with no annual cap
Annual caps limit total exposure, and they’re lower for small businesses (those with average annual gross receipts of $5 million or less over the prior three tax years) than for larger ones.9Internal Revenue Service. IRM 20.1.7 Information Return Penalties The practical takeaway is the per-return number: correcting inside that first 30-day window drops your exposure from $340 to $60 per 1099, which by itself justifies treating a CP2100 as urgent.
Preventing the Next Mismatch
The cheapest fix is one you make before filing. The IRS TIN Matching program lets you check name/TIN combinations against IRS records at no charge, either interactively (up to 25 at a time, with instant results) or in bulk (up to 100,000 per file, with results within 24 hours).10Internal Revenue Service. Taxpayer Identification Number (TIN) Matching Access runs through the IRS e-Services portal and requires registration.11Internal Revenue Service. Taxpayer Identification Number (TIN) Matching Tools Running each new vendor through TIN Matching when they submit their W-9 catches most data entry errors before they become penalty exposure.
Requesting Penalty Abatement for Reasonable Cause
If penalties are already assessed, you can ask for abatement on reasonable cause grounds. The standard has two parts, and both must be met. First, a significant mitigating factor or an event beyond your control caused the failure — a system conversion that corrupted TIN data, a disaster that destroyed records, something of that magnitude. Second, you acted in a “responsible manner” both before and after the failure: you took steps to prevent the error, tried to fix it once you knew, and corrected it as quickly as possible.12eCFR. 26 CFR 301.6724-1 – Reasonable Cause Fail the responsible-manner element and the rest doesn’t matter.
The IRS weighs your compliance history over the preceding three years, how long the noncompliance lasted, whether the event was foreseeable, and what you did despite the circumstances.13Internal Revenue Service. IRM 20.1.1 Introduction and Penalty Relief Blaming an accountant or a payroll service generally doesn’t work; the IRS treats the filing obligation as non-delegable.
Send a written statement to the address on the penalty notice. Identify the specific penalty, lay out the facts supporting reasonable cause, and sign a perjury declaration.12eCFR. 26 CFR 301.6724-1 – Reasonable Cause The strongest requests include a timeline of when the problem arose and what you did about it, along with documentation: corrected filings, system logs, B-Notice mailing records — anything showing you moved promptly once the issue came to light.