Every vendor payment your business makes is tied to a Taxpayer Identification Number (TIN). When that number is wrong, the IRS flags it, and the penalties follow.
A missing or mismatched TIN can trigger IRS penalties and backup withholding on future payments, pulling you into a B-Notice compliance loop that can take months to resolve.
This guide explains what a TIN is, the types your business will encounter, and how to make sure what you collect holds up under IRS scrutiny.
What Is a TIN?
A TIN is a unique nine-digit number assigned to every individual, business, or other entity that has a tax obligation in the United States. The IRS uses it to track tax filings, match income reported on information returns against what taxpayers report on their own returns, and identify who owes tax and who is owed a refund.
The term TIN is an umbrella term. It does not refer to a single document or number type. Instead, it covers several identification numbers, each issued for a specific purpose and type of taxpayer. Your Social Security Number is a TIN, as is the EIN your vendor provides on a W-9.
For your business, a TIN is more than an identifier. It links every reported payment to how the IRS validates that transaction. If that link breaks, your filing does too.
Any time a TIN appears on a tax form, including a 1099, W-2, or W-9, the IRS uses it to confirm the identity of the person or business named on that form. If the name and TIN do not match IRS records, the filing is flagged.
The Five Types of TINs and When Each Applies
| TIN Type | Full Name | Issued By | Who Uses It |
| SSN | Social Security Number | Social Security Administration | US citizens, permanent residents, authorized workers |
| EIN | Employer Identification Number | IRS | Businesses, partnerships, LLCs, nonprofits, trusts |
| ITIN | Individual Taxpayer Identification Number | IRS | Non-resident and resident aliens ineligible for an SSN |
| PTIN | Preparer Tax Identification Number | IRS | Paid tax preparers filing returns on behalf of clients |
In day-to-day operations, most businesses deal primarily with SSNs and EINs when collecting W-9s and preparing 1099s.
An individual contractor will typically provide an SSN. A business entity will provide an EIN.
ITINs appear when working with foreign individuals who have US tax obligations. If you collect an ITIN, confirm that it is still active, as ITINs expire if unused for three consecutive years.
PTINs are used exclusively by paid tax preparers and do not appear in standard vendor payment workflows like W-9 collection or 1099 filing.
TIN vs EIN: What Is the Difference?
This is one of the most common and costly points of confusion in 1099 filing. A TIN is the broad category.
EIN is one specific type of TIN used for business entities. So when you ask a vendor what their TIN is, they will provide whichever number applies to their entity type.
The key compliance requirement is that the name and TIN combination must match IRS records exactly.
A common mismatch scenario: A sole proprietor provides a business name but uses their SSN. The IRS matches SSNs to legal names, not trade names, which results in a failed match.
When Your Business Needs to Collect and Use a TIN
TIN collection and usage happen at multiple points across your payment and reporting workflow.
On Form W-9. During vendor onboarding, you collect a W-9 form that includes the payee’s legal name, entity type, and TIN. This becomes the source record for every 1099 you file, which is why accuracy at this stage is critical.
On Form 1099. Every 1099 you file includes both your and the payee’s TIN. The IRS uses this data to match reported payments against tax filings, making accuracy non-negotiable.
In backup withholding. If a payee does not provide a TIN, provides an incorrect one, or the IRS flags a mismatch, you must begin 24% backup withholding on payments until the issue is resolved.
In W-2 filing. Employees provide their SSN at onboarding, and that number is used in every W-2 filing for payroll reporting.
In all of these scenarios, the key is timing. TINs should be collected and validated at onboarding, not after payments begin or errors surface.
What Happens When a TIN Is Wrong or Missing
An error on a 1099 triggers an IRS TIN matching check, and if the name and TIN do not align with IRS records, the return is flagged, and a notice is issued.
The IRS issues a CP2100 or CP2100A notice listing each mismatched record. From the notice date, you have 15 business days to send a B-Notice requesting a corrected W-9. If the issue is not resolved within 30 business days, you must begin backup withholding on future payments.
Failure to act on a CP2100 notice can lead to penalties under IRS Sections 6721 and 6722:
| When The Correction Is Made | Penalty Per Return |
| Within 30 days of the filing deadline | $60 |
| Between 31 days and August 1 | $130 |
| After August 1 or never corrected | $340 |
| Intentional disregard | $690 |
These penalties apply per form, per year. Most mismatches are caused by simple issues such as data entry errors, outdated names, sole proprietors using trade names instead of legal names, and transposed digits in an SSN or EIN.
How to Verify a TIN Before You File
The IRS offers a TIN Matching program through its e-Services platform, and although this can be a useful tool for those who already have access or are doing a limited number of checks, the system has its limitations.
In order to gain access to the IRS tool, you’ll need an eServices account or apply for one on the IRS website. In addition, the tool is limited in the number of interactive checks that can be done (limited to 25 records at a time).
For businesses that need real-time verification or workflow integration, tools like TINCheck allow you to validate name and TIN combinations at onboarding or in bulk before filing. This helps catch mismatches early, before they appear on a 1099 or trigger IRS notices.
Verify Your TINs Before They Become a Problem
Every 1099 you file submits a name and TIN combination to the IRS. If it does not match, it can trigger notices, withholding, and penalties.
Collecting a W-9 is the first step. Verifying the TIN is what keeps your reporting accurate.
TINCheck by Sovos allows you to verify payee TINs in real time or in bulk before filing, so mismatches are caught early rather than surfacing in a CP2100 notice later.
Start verifying TINs with TINCheck today.
FAQs
What is the difference between a TIN and a Social Security Number?
An SSN is one type of TIN. TIN is the umbrella term that includes SSNs, EINs, ITINs, and PTINs.
What TIN should a contractor provide on a W-9?
It depends on their entity type. Individuals provide SSNs, while businesses provide EINs. The name must match IRS records for that number.
What happens if a vendor refuses to provide a TIN?
You must begin backup withholding at 24% and document your attempts to collect the TIN.
Can a TIN expire?
ITINs expire after three years of non-use. EINs and SSNs do not expire, but associated names must remain accurate.
What is a TIN mismatch, and how do I fix it?
A TIN mismatch occurs when the name and TIN you report do not match IRS records. Common causes include typos, outdated names, or using a trade name instead of a legal name. To fix it, send a B-Notice, collect a corrected W-9, update your records, and file a corrected 1099 if needed. Running a TIN check before filing helps prevent this.