How to Verify a Supplier’s GST/QST Registration Number — Montreal CPA Firm Near You

Verifying a supplier’s GST and QST registration numbers is one of the most important — yet most overlooked — responsibilities for any Quebec business. If you claim Input Tax Credits (ITCs) or Input Tax Refunds (ITRs) based on invoices from a supplier who is not properly registered for GST/QST, Revenue Québec and CRA can deny the credit, reassess your return, and charge penalties and interest. Many businesses don’t realize that the taxpayer is responsible for validating supplier tax numbers, not the government. This guide explains how to verify GST and QST numbers correctly using the same audit-proof procedures Mackisen CPA Montreal uses for its clients.

Why This Matters
If you claim ITCs or ITRs from a supplier who doesn’t have valid tax registration, the government assumes your claim is invalid. Even if the supplier made an honest mistake, YOU lose the refund. Revenue Québec also treats repeated claims from unregistered suppliers as a compliance red flag, increasing your chance of future audits.

Legal and Regulatory Framework
GST registration falls under the Excise Tax Act, and QST registration falls under Quebec’s Tax Administration Act.
A valid invoice for GST/QST must include:
Supplier’s legal name
Supplier’s GST number (RT)
Supplier’s QST number (TQ)
Invoice number and date
Description of goods/services
Tax amounts separately listed
Hickman Motors (1997, SCC) establishes that the taxpayer bears the burden of proof.
Canderel (1998, SCC) confirms filings must reflect commercial reality.
Lac d’Amiante (2001, SCC) confirms that RQ can deny credits if documentation is incomplete or if tax numbers are invalid.

A business claims $22,000 in ITRs over two years from subcontractors. During a routine review, RQ checks the TQ numbers on those invoices and discovers two subcontractors were not legally registered at the time of invoicing. Revenue Québec denies the entire $22,000 refund and issues interest charges. The business is shocked — the subcontractors collected QST, yet the credits are denied because the numbers were invalid. This scenario happens frequently because businesses assume the supplier is compliant.

Learning Section: What a Valid GST/QST Number Looks Like

GST Registration Number (CRA)
Format: 123456789 RT0001

QST Registration Number (Revenue Québec)
Format: 1234567890 TQ0001

If the format is incorrect, the number is invalid.

SEO Learning: Primary and Secondary Keywords
Primary: verify GST number Quebec, verify QST number, how to check supplier tax number Montreal.
Secondary: GST QST invoice rules, verify RT TQ registration, Revenue Québec supplier verification.

How to Verify a GST Number (CRA)
Use the CRA GST Registry Lookup Tool:
Search by Business Number
Confirm the RT0001 program account is active
Verify the legal business name matches the invoice
Check the effective registration date
Take a screenshot for your records
CRA’s registry is updated frequently and is considered authoritative.

How to Verify a QST Number (Revenue Québec)
Use the Revenue Québec “Validate a QST Number” tool:
Enter the TQ number
Confirm that the business is registered
Verify that the legal name matches the invoice
Check that the registration was active on the invoice date
Download or screenshot the confirmation
RQ’s system instantly checks for registration errors.

Documentation Section
You must keep:
Supplier invoices
Proof of payment
GST/QST validation screenshots
Supplier contracts
Merchant processor statements
Bank statements
Reconciliation worksheets
All documentation must be kept for six years in case RQ or CRA requests proof that you validated the tax numbers.

Common Mistakes Made by Businesses
Paying suppliers without checking tax numbers
Assuming sole proprietors automatically have RT/TQ numbers
Accepting invoices missing RT/TQ numbers
Using credit card slips instead of invoices
Not confirming if registration was active at invoice date
Claiming ITCs/ITRs on invalid invoices
Not performing periodic supplier verification
These errors cause denied refunds, interest charges, and follow-up audits.

Winning With Revenue Québec and Canada
Mackisen performs full verification of all supplier tax numbers during bookkeeping and before filing GST/QST returns. We maintain a validated tax-number binder with screenshots and documentation that can be presented instantly during a review or audit. If RQ challenges a supplier’s registration, we handle communication and provide proof of verification to defend your credits. Our system ensures your ITCs/ITRs are fully protected.

Mackisen Service Hub
We provide:
Supplier tax-number verification
GST/QST documentation audits
Invoice compliance checks
Corrected filings
Audit-defense support
Training for staff to verify tax numbers properly
Threshold and registration monitoring for subcontractors
Our system eliminates refund denial risk linked to supplier compliance.

Why Mackisen
With over 35 years of CPA and audit experience, Mackisen CPA Montreal ensures every tax credit you claim is properly supported, verified, and defensible. We protect your business from denied refunds, costly reassessments, and supplier-related audit traps.