Finance Index
What documents are required to onboard a new vendor in the US?
Reference guide to vendor onboarding documents required, including vendor records, onboarding requirements, compliance checks, fraud controls, and payment readiness.
For a US vendor, the practical minimum is: a completed W-9 (legal name, TIN, tax classification, signature), verified banking details for electronic payment, remit-to address, and a primary contact. Risk-based additions include certificates of insurance, signed contracts or MSAs, licenses, and industry-specific documents like lien waivers for construction subcontractors.
At a Glance
| Aspect | Short Answer | Why It Matters |
|---|---|---|
| What documents are required | For a US vendor, the practical minimum is: a completed W-9 (legal name, TIN, tax classification, signature), verified banking details for electronic payment, remit-to address, and a primary contact. | Reduces payment errors, timing issues, and reconciliation cleanup. |
| Vendor onboarding | Stop accepting W-9s and voided checks as email attachments - email is where banking fraud starts and where SSNs leak. | Reduces payment errors, timing issues, and reconciliation cleanup. |
| Related terms | Tier it: every vendor gets the W-9/W-8 and banking-verification requirement. | Keeps vendor records and payment decisions reliable. |
| Voided check used | A voided check was the traditional way to evidence account and routing numbers. | Keeps evidence clear and reduces control risk. |
| Vendor impact | Risk-based: vendors performing physical work on-site, transportation, construction, and anyone whose failure creates liability for you. | Keeps vendor records and payment decisions reliable. |
How do I collect vendor onboarding documents securely?
Stop accepting W-9s and voided checks as email attachments - email is where banking fraud starts and where SSNs leak. Use a secure portal or document-collection workflow where the vendor uploads directly into the vendor record, access is role-restricted, and every submission is logged. If email is unavoidable, restrict who can receive and store the documents and move them out of inboxes immediately.
Which documents should be required vs optional by vendor type or spend level?
Tier it: every vendor gets the W-9/W-8 and banking-verification requirement. Services vendors on your premises add COI. Regulated trades add licenses. High-spend or contract vendors add the executed agreement. Requiring everything from everyone slows onboarding and trains the business to bypass you; requiring too little from risky vendors is how losses happen.
What is a voided check used for, and is a bank letter an acceptable substitute?
A voided check was the traditional way to evidence account and routing numbers. A bank letter on letterhead is an acceptable substitute - but neither proves the vendor controls the account, which is why independent bank verification matters more than either document.
Should we require certificates of insurance from every vendor or only certain categories?
Risk-based: vendors performing physical work on-site, transportation, construction, and anyone whose failure creates liability for you. Requiring COIs from your software vendor adds friction without protection. Set coverage minimums by category in policy.
How do I verify a vendor's business legitimacy during onboarding?
Layer cheap checks: TIN match against the W-9 name, Secretary of State registration lookup, a real web/physical footprint, independent phone verification of contact details, and a sanctions screen. No single check is conclusive; the combination is hard to fake.
What is a vendor information form and what fields should it include?
It's the structured intake document for new vendors: legal name and DBA, entity type, EIN/SSN, addresses (physical and remit-to), contacts, banking details, payment terms requested, and certifications. Every field you don't capture at intake becomes a follow-up email later.
Vendor's W-9 name doesn't match their invoice name - which do I use?
Set the vendor up under the W-9 legal name (line 1) - that's what the IRS matches at 1099 time - and record the invoice/trade name as the DBA. If the mismatch is unexplained, resolve it with the vendor before activation.
How do I handle dba names vs legal names in vendor setup?
Legal name is the master record name and the 1099 name; DBA goes in a dedicated trade-name/alias field so invoice matching still works. Never 1099 a DBA when the W-9 shows a different legal entity.
Do we need a signed contract or msa on file before paying a vendor?
Not legally for routine purchases - the invoice and PO can constitute the agreement - but for services, recurring spend, or anything with liability exposure, a signed agreement should be an onboarding requirement, and its absence should be a conscious exception, not a default.
What extra documentation do construction subcontractors need at onboarding?
COI with required limits and additional-insured wording, active trade licenses, W-9, lien waiver process agreement, and on public work, prevailing-wage/certified-payroll compliance. Expirations matter as much as collection - an expired COI on file is a false sense of security.
Stampli perspective
Stampli lets customers build customizable onboarding forms by vendor type, so a construction subcontractor and a SaaS provider face different document requirements. Vendors upload W-9s, banking details, and insurance through the secure self-service portal, documents attach to the vendor record with an audit-ready history, and missing or expired mandatory documents can automatically block invoices or payments.