A vendor invoices you $3,500 for consulting work. You pay it. Three months later, you're filing 1099s and realize you never got a completed W-9 — you don't have a tax ID number, you're not sure if the vendor is a corporation (which would exempt them from a 1099 entirely), and now you're staring down a choice: chase down paperwork after the fact, or start withholding 24% from a contractor who already cashed the check.
This is one of the most common — and most avoidable — headaches in small business bookkeeping. Backup withholding exists specifically to solve the problem of unreported income, and the IRS puts the burden of prevention squarely on the business making the payment. The good news is that the entire problem disappears with one simple habit: collect the W-9 before the first dollar goes out the door, not after.
Here's how to build a vendor-onboarding process that keeps you out of the 24% withholding trap and off the IRS's notice list.
What Backup Withholding Actually Is
Backup withholding is the IRS's mechanism for making sure it eventually collects tax on income that would otherwise go unreported. If you're required to file an information return (like a 1099-NEC or 1099-MISC) for a payment, and something is wrong with the payee's taxpayer identification — missing, incorrect, or unverifiable — the IRS requires you to withhold 24% of future payments to that vendor and remit it directly to the Treasury.
There are two main paths that lead to backup withholding:
- BWH-B (the one that hits most small businesses): The vendor didn't give you a correct Taxpayer Identification Number (TIN) — or didn't give you one at all.
- BWH-C: The vendor has a history of underreporting interest or dividend income, or failed to certify they're not subject to withholding. This one is rarer for typical vendor payments and more relevant to financial institutions.
For a typical small business paying contractors, freelancers, and vendors, BWH-B is the scenario to worry about — and it's entirely preventable with good paperwork.
The 2026 Threshold Change (and Why It Doesn't Let You Off the Hook)
If you've heard that the 1099 reporting threshold changed this year, you heard right: for payments made on or after January 1, 2026, the threshold for filing Form 1099-NEC jumped from the decades-old $600 to $2,000 per vendor, per calendar year, and it will now adjust for inflation annually.
That's a meaningful compliance simplification — fewer forms for the smallest, most occasional vendors. But it changes nothing about when you need a W-9. Here's why: you rarely know at the start of a relationship whether a vendor will cross $2,000 by December 31. A freelancer you hire for a $400 one-off project in February might come back in October for another $1,800 of work. If you didn't collect a W-9 up front, you're now scrambling in January to get one — and if the vendor is slow to respond or unreachable, you're filing with missing information or starting backup withholding after the fact, which is far messier than doing it retroactively on a single payment.
The rule of thumb: collect a W-9 from every vendor you pay for services, regardless of the amount, before you issue the first payment. You can always decide later that a vendor didn't cross the filing threshold. You can't easily go back and get a signature after the relationship has ended.
Building the Vendor-Onboarding Checklist
The single highest-leverage fix here is procedural, not technical: make W-9 collection a hard gate before a vendor gets paid, the same way you'd gate a new employee's first paycheck on a completed I-9.
1. Add W-9 collection to your intake form. Whether you use a vendor portal, a simple onboarding email, or a shared intake spreadsheet, the W-9 request should go out with the very first vendor communication — alongside the contract or purchase order, not after the invoice arrives.
2. Validate the form before you file it away, not before you pay. A W-9 isn't valid just because someone filled it out. Check for:
- A signature and date (an unsigned W-9 is not a valid certification)
- A completed TIN — either a Social Security Number or an Employer Identification Number, not left blank
- A checked federal tax classification box (individual/sole proprietor, C-corp, S-corp, partnership, LLC, etc.)
- Consistency between the name on line 1 and the TIN provided — a business name with an SSN, or vice versa, is a common source of mismatches later
3. Note the entity type — it determines whether you even need to send a 1099. Payments to most corporations (C-corp or S-corp) are generally exempt from 1099-NEC reporting, with common exceptions for attorney fees and medical/health care payments, which get reported regardless of corporate status. Capturing this at onboarding saves you from generating unnecessary forms — and from mistakenly treating an LLC taxed as an S-corp the same as a sole proprietor LLC.
4. Run the TIN through the IRS TIN Matching Program before year-end filing. The IRS offers a free tool through its e-Services platform that lets you check a name/TIN combination against IRS records before you file. Interactive matching returns results immediately for small batches; bulk matching handles larger vendor lists within 24 hours. Running this check in Q4 — before you generate 1099s — catches typos and mismatched entity names while there's still time to fix them, instead of finding out from an IRS notice next year.
5. Store W-9s centrally and set a re-verification reminder. A W-9 doesn't expire, but vendor information changes — name changes, entity conversions (a sole proprietor incorporates), or address updates. A light-touch practice is to ask long-term vendors to reconfirm their W-9 every two to three years, or whenever you notice a legal name change on an invoice.
What Happens If You Skip This — the CP2100 and B-Notice Process
If you file 1099s with a TIN that doesn't match IRS records, you don't find out immediately. The IRS matches filed information returns against its records after the filing season, and if there's a mismatch, it sends you a CP2100 notice (or CP2100A if you filed fewer than 50 returns with errors). This is commonly called a "B-notice."
Once you receive one, the clock starts:
- You must send the affected vendor a first B-notice and a new W-9 request within 15 business days of receiving the CP2100.
- If the vendor doesn't respond with a corrected, valid W-9, you're required to begin backup withholding at 24% on any future payments, no later than 30 business days after you received the notice.
- If you get a second B-notice for the same vendor within a three-year window, the rules get stricter: you must begin backup withholding immediately, and merely receiving a new W-9 from the vendor isn't enough to stop it — the vendor has to go directly to the IRS or Social Security Administration to resolve the underlying mismatch before withholding can stop.
On top of the operational disruption of withholding, there are separate penalties for filing incorrect information returns — ranging roughly from $60 to $680 per form depending on how quickly the error is corrected and whether the IRS considers it intentional disregard. Notably, the penalty clock starts at the original filing deadline (January 31 for 1099-NEC), not when you receive the notice — so by the time a CP2100 lands in your mailbox, you may already be past the cheapest correction tier.
None of this is a fair fight if you're starting from a folder of half-completed W-9s. It's a very fair, very manageable process if every vendor file already has a valid, signed form on record.
What To Do When a Vendor Refuses to Provide a W-9
Occasionally a vendor — usually a smaller contractor unfamiliar with the process — will drag their feet or refuse outright. You still have obligations here: you cannot simply skip filing the 1099. The correct response is to file the form with whatever information you have (leaving the TIN blank or noting it as unavailable) and to begin backup withholding immediately at 24% on payments to that vendor until they provide a valid TIN. Document your requests (dated emails or letters asking for the W-9) so you can show the IRS you made a good-faith effort if the issue is ever questioned.
Keep Your Financial Records Audit-Ready from Day One
A clean vendor-onboarding process is really just an extension of good bookkeeping — the same discipline that keeps your chart of accounts accurate keeps your 1099 filings accurate too. Every payment tied to a verified vendor record, with the entity type and TIN status captured up front, turns January's 1099 season from a scramble into a formality. Beancount.io brings that same rigor to your day-to-day financial records: plain-text, version-controlled accounting that gives you a transparent, auditable trail with no vendor lock-in and no black-box software. Get started for free and see why developers and finance-minded business owners are switching to plain-text accounting.