How to Object to an HST/GST Assessment in Ontario

Getting a CRA assessment or reassessment for GST/HST can feel different from an income tax reassessment — the numbers often relate to a business's day-to-day operations, disallowed input tax credits, or an audit of specific transactions. But the underlying process to object to HST GST assessment results follows the same basic legal framework as other federal tax disputes, run under the Excise Tax Act rather than the Income Tax Act.

Ontario's HST is a federal tax — even though it includes a provincial component, the CRA (not the Ontario Ministry of Finance) administers and audits it, and disputes go through the same federal system as income tax objections and appeals.

Here's how the process generally works, step by step.

Step 1: Review the Notice of (Re)Assessment Carefully

Before you object to anything, understand exactly what CRA changed and why. A GST/HST reassessment might deny input tax credits (ITCs) you claimed, add tax CRA says should have been collected, or adjust how a specific supply was characterized. The reasons for the reassessment — often included with the notice or available on request — tell you what you actually need to address in your objection.

Step 2: Confirm Your Objection Deadline

A strict deadline applies to filing a Notice of Objection to a GST/HST assessment, and it runs from the date the assessment was sent — not from when you happen to open the letter. This deadline is calculated under different rules than the income-tax objection deadline, so don't assume the two are the same. Check the deadline printed on your notice, and if it's unclear, confirm the current rule before you do anything else.

Step 3: File a Written Notice of Objection

Your objection should clearly identify the assessment being disputed and set out the reasons you disagree, supported by relevant facts and documentation — invoices, contracts, and records showing how the disputed supply, credit, or transaction was actually treated. This is an administrative filing with the CRA, not a court proceeding, and it must happen before you have any right to appeal to the Tax Court of Canada.

Step 4: CRA Appeals Reviews Your File

A CRA Appeals officer — someone not involved in the original audit — reviews your objection and supporting materials. This stage can result in the assessment being confirmed, varied, or vacated. It's also often the most realistic opportunity to resolve the dispute without going to court.

Step 5: If CRA Confirms the Assessment (or Stays Silent)

If CRA issues a Notice of Confirmation you still disagree with, you generally have 90 days from that notice to appeal to the Tax Court of Canada. If CRA simply doesn't respond to your objection at all, GST/HST rules give you a longer inaction window than income tax disputes do — you gain the right to appeal after CRA has failed to respond for 180 days, rather than the shorter period that applies to income tax objections (figures as of mid-2026; verify the current rule before relying on it).

Step 6: Appeal to the Tax Court, If Necessary

GST/HST appeals can proceed under the Tax Court's Informal Procedure where the amount in dispute is modest — currently up to $50,000 for GST/HST matters (figures as of mid-2026; verify the current limit) — or under the General Procedure for larger or more complex disputes.

What Commonly Triggers a GST/HST Reassessment

CRA GST/HST audits and reassessments often focus on a recurring handful of issues:

• Input tax credits claimed without adequate supporting invoices
• Supplies characterized as exempt or zero-rated that CRA views as taxable
• Discrepancies between reported sales and other records, such as bank deposits or third-party information
• Errors in how a business allocates GST/HST collected between reporting periods

Understanding which of these applies to your file helps you gather the right evidence before you draft your objection.

Frequently asked questions