Vendor payment compliance is the intersection of accounts payable operations and tax law. Finance teams who get this wrong face year-end scrambles to collect missing W-9s, backup withholding obligations they were not tracking, and 1099 penalties that are entirely avoidable.
This guide covers the compliance obligations that finance teams own and the controls that prevent the most common problems.
The W-9 Gate
The single most important control in vendor payment compliance is a hard gate that prevents any payment to a new vendor until a valid W-9 is on file.
This sounds obvious. It is not universally practiced. The typical failure pattern: a vendor is engaged, starts work, submits an invoice. The invoice is approved and goes to AP. AP pays it. Someone remembers to collect the W-9 later. Or they do not.
By the time January arrives and 1099-NECs need to go out, the vendor may be unresponsive, may have changed their business information, or may have been a sole proprietor who used a personal SSN that they are now reluctant to provide.
The fix: No vendor record is created in your payment system until a W-9 is collected and verified. The operational team that onboards vendors owns the W-9 collection. AP does not process invoices from vendors without a TIN on file.
Backup Withholding
Backup withholding is a 24% withholding obligation on payments to vendors when:
- The vendor fails to provide a TIN when required
- The IRS notifies you (via a B Notice) that the TIN the vendor provided does not match their records
- The vendor fails to certify their TIN exemption from backup withholding
The backup withholding is remitted to the IRS using Form 945. It is reconciled against the vendor's annual tax return — so it is not a permanent cost to the vendor, but it is a significant administrative burden and a source of vendor relationship friction.
The B Notice process: When the IRS sends a CP2100 or CP2100A notice identifying mismatched TINs in your 1099 filings, you have 15 business days to send a first B Notice to the affected vendor requesting a correct TIN. If the TIN is not corrected within 30 days, you must begin backup withholding. If you receive a second B Notice within three calendar years for the same vendor, you must begin backup withholding immediately.
The volume of B Notices you receive is directly correlated with how rigorously you verified W-9 information at collection. Companies that collect W-9s casually receive more B Notices.
The $600 Threshold and What It Actually Covers
The $600 threshold for 1099-NEC reporting is widely known and widely misunderstood. Some facts:
It applies per calendar year, per payee. Payment number fourteen to a vendor does not retroactively exempt the first thirteen. Once aggregate payments exceed $600, all payments are reportable.
It applies to services, not goods. Payments to a vendor for physical goods (excluding merchandise) are generally not subject to 1099 reporting. Payments for services — labor, consulting, contracting — are.
Corporations are generally exempt. Payments to C-corps and S-corps do not require a 1099-NEC in most circumstances. However, payments to attorneys and medical/healthcare providers require a 1099-MISC regardless of corporate status.
It does not apply to payroll. Employee wages are reported on W-2s. This guide covers non-employee payments only.
Payment Hold Policies for Missing Documentation
Finance teams should have a written policy specifying when payments are placed on hold pending compliance documentation. Recommended policy elements:
W-9 missing: Hold all payments until a valid W-9 is received and verified.
Backup withholding triggered: Begin withholding 24% of payments, remit quarterly on Form 945, document the withholding in the payment record.
Expired insurance for on-site vendors: Coordinate with operations for work hold decisions; finance holds payment for any invoices covering work performed during the lapse period until the compliance question is resolved.
Tax exemption certificate expired: Hold tax-exempt treatment; charge sales tax on invoices until a valid certificate is on file.
Year-End 1099 Preparation
Start the year-end 1099 process in November, not January. By November, you can identify vendors who are approaching the $600 threshold and may not have a W-9 on file, chase outstanding W-9s while there is still time to receive them before the filing deadline, and verify TINs through the IRS TIN Matching Program before filing.
The IRS TIN Matching Program is a free service that lets you verify name/TIN combinations before filing 1099s. Using it eliminates the majority of B Notices before they happen.
Building Compliance Into AP Processes
The compliance controls that matter most in vendor payment compliance are operational controls, not financial controls. They happen at vendor onboarding (W-9 collection), at payment setup (W-9 verification), and at the point of processing (hold policies for missing documentation).
Finance teams that own payment compliance but do not own vendor onboarding need a formal handoff: compliance documents collected at onboarding, verified information passed to AP, and a clear status indicator in the payment system showing which vendors have complete documentation on file.
A vendor compliance platform creates this handoff automatically — the payment clearance flag in your AP system is driven by the document status in the compliance system, with no manual coordination required.