How to Dispute a CRA Tax Decision in Canada (Assessment, Reassessment, GST/HST)

Receiving a Canada Revenue Agency (CRA) Notice of Assessment or Notice of Reassessment can be stressful—especially when the change increases what you owe, denies deductions, or reduces refunds. The good news is that Canada has a structured dispute process that allows taxpayers to challenge CRA decisions in an organized, evidence-based way.

This guide explains how to dispute a tax decision in Canada, including: what to do first, how to file a Notice of Objection, what documents to include, key deadlines, and when (and how) to take the matter to the Tax Court of Canada. It’s written for Canadian individuals, self-employed taxpayers, and business owners who want a clear, practical roadmap.

1) What “tax decisions” can you dispute?

A “tax decision” typically refers to a CRA decision that affects the amount of tax, penalties, or interest you owe (or your refund/credits). Common examples include:

• Income tax assessments/reassessments (personal or corporate)
• Notices of determination/redetermination (certain tax matters and credits)
• GST/HST assessments/reassessments (input tax credits denied, net tax adjusted, penalties assessed)

CRA’s dispute system generally starts with an objection (the formal first step) and may continue to a court appeal if the issue is not resolved.

2) Step one: confirm what changed and why

Before you file anything, slow down and identify exactly what CRA changed. Many disputes are easier to resolve when you isolate the issue (or issues) rather than treating the notice as one big problem.

Quick review checklist

• What line(s) or schedule(s) changed?
• What reason did CRA provide?
• Was it a missing document, a matching issue, or a disagreement about eligibility?
• Is the dispute about tax owed, penalties/interest, or both?

If the issue is missing documentation or a misunderstanding of facts, the fastest path is often to contact CRA or submit supporting information promptly. However, do not assume informal back-and-forth will protect your legal deadlines—always track your objection time limits.

3) Step two: watch the deadlines (the most important part)

Dispute rights are heavily deadline-driven. Missing a time limit can reduce your options or force you to request an extension.

Key deadlines (high-level)

• Corporations: CRA states you generally have 90 days from the date of the notice of assessment/reassessment to file an objection.
• GST/HST: CRA states the time limit for filing a GST/HST objection is 90 days from the date of the notice of (re)assessment.
• Income tax (individuals): CRA explains that, depending on your situation, you may have one year after the filing deadline or 90 days from the assessment/reassessment date (whichever is later) in many cases—so you must confirm your specific limitation period.

If you missed the deadline, you may still have options (for example, requesting an extension), but you should act immediately and document why you are late. CRA’s guidance explains extension pathways and timelines.

4) Step three: file a formal Notice of Objection (the core dispute process)

If the matter cannot be resolved informally—or if you want to preserve your rights—you typically move to a Notice of Objection. CRA describes objection rights and the objection/appeal framework in its dispute guidance.

A) What is a Notice of Objection?

A Notice of Objection is a formal statement that you disagree with the CRA’s decision and want an independent review within CRA’s Appeals area. It’s the standard entry point to formally dispute a CRA assessment or reassessment.

B) Which forms are commonly used?

• Income tax objection (Notice of Objection – Income Tax Act): CRA provides Form T400A for filing an objection.
• GST/HST objection: CRA provides Form GST159 (Notice of Objection – GST/HST).

CRA also indicates you may be able to file electronically through CRA portals in many situations.

C) What to include in a strong objection (what makes it persuasive)

A professional-quality objection reads like a concise case file: clear issues, clean facts, and organized proof.

Include:

1. The decision you’re disputing

• Identify the notice type (assessment/reassessment), the date, and the account (T1/T2/GST/HST).

2. The issues (separate them clearly)
   Example:

• Issue 1: CRA denied business advertising expense of $X
• Issue 2: CRA reduced ITCs on specific invoices
• Issue 3: CRA assessed a penalty for late remittance

3. Your facts (timeline + documents)
   Use objective facts: who/what/when/where/how much. Avoid emotion; “unfair” rarely helps in an objection.
4. Your position (why CRA is wrong)
   Explain whether CRA:

• misunderstood the facts,
• ignored key documents, or
• applied a rule incorrectly.

5. Your calculations (show the correct numbers)
   If CRA added income, disallowed expenses, or denied credits, show your corrected computation.
6. Your supporting evidence (organized)
   Attach only relevant documents—and label them:

• contracts, invoices, receipts, bank proof,
• bookkeeping ledgers,
• mileage logs,
• GST/HST working papers,
• correspondence from suppliers/clients (if relevant).

CRA’s dispute guidance emphasizes clearly outlining facts and reasons, and using the appropriate objection route/forms.

5) What happens after you object?

After an objection is filed, CRA’s Appeals process reviews the matter. Timelines vary by complexity and volume. CRA publishes information about processing times and complexity levels for income tax and GST/HST objections, and notes delays due to higher-than-normal volumes.

During the review, CRA may:

• request more information,
• ask clarifying questions,
• propose a settlement or adjustment, or
• confirm the assessment as issued.

A practical tip that helps

Treat your objection like a “living file.” If CRA asks for more information, respond quickly and keep your evidence package consistent, paginated, and easy to reference. The easier your file is to review, the faster and cleaner resolution tends to be.

6) If you still disagree: appeal to the Tax Court of Canada

If CRA confirms its decision (or you do not receive a decision within certain timelines), you may be able to appeal to the Tax Court of Canada.

CRA explains that:

• You generally have 90 days from the date of the notice of confirmation/reassessment/redetermination to appeal to the Tax Court of Canada.
• You may also appeal if CRA has not issued a decision within 90 days from the date you filed your income tax objection or within 180 days from the date you filed your GST/HST objection.

This is where professional representation and well-structured evidence become especially important, because court processes have their own rules, filings, and standards.

7) Don’t confuse “disputing the tax” with “asking for penalty/interest relief”

Sometimes you agree the underlying tax is correct but believe CRA should reduce or cancel penalties and interest due to circumstances beyond your control (serious illness, disaster, CRA delays, hardship, etc.). In those situations, a taxpayer relief request may be appropriate.

CRA outlines the taxpayer relief approach and provides Form RC4288 for requesting relief to cancel or waive penalties and interest.

Important: a taxpayer relief request typically does not replace an objection if your goal is to dispute the correctness of the assessment itself—they are different tools used for different problems.

8) Common reasons CRA disputes fail (and how to avoid them)

1) Missing deadlines

Deadlines are non-negotiable in most cases. Track them the moment you receive the notice.

2) Vague objections

A strong objection is specific: what CRA changed, what you believe is correct, and why.

3) Weak documentation

The most persuasive disputes are evidence-driven. If you claim an expense or ITC, you should be able to prove it with clear documents and business purpose.

4) No calculations

If you don’t show the “correct” amount, CRA has less to work with. Provide clean math.

5) Mixing legal arguments with hardship arguments

Hardship is generally more relevant to taxpayer relief than to the core objection about correctness.

9) A professional checklist to prepare your dispute package

Gather:

• The CRA notice (assessment/reassessment/determination) and date
• The return(s) involved (T1/T2/GST/HST)
• CRA audit/review letters and working papers (if applicable)
• Receipts/invoices + proof of payment (bank/credit statements)
• Contracts and business correspondence (if relevant)
• A one-page issue summary + timeline
• Your corrected calculations and schedules

Then:

• Separate issues into sections
• Label evidence as Appendix A, B, C…
• Reference each appendix directly in your explanation

This is the same “clean file” approach used in strong professional submissions—easy to read, easy to verify.

10) Need help disputing a CRA decision? BOMCAS Canada can support you

Disputing a CRA tax decision is rarely about “arguing”—it’s about deadlines, documentation, and precise explanations. BOMCAS Canada can help you:

• Review the CRA notice and identify exactly what changed
• Confirm the best path (adjustment vs. objection vs. taxpayer relief)
• Prepare a well-structured objection package (facts, calculations, evidence)
• Support GST/HST objections and corporate reassessment disputes
• Organize records to prevent repeat reassessments

Contact BOMCAS Canada
Phone: 780-667-5250
Email: info@bomcas.ca
Website: https://bomcas.ca

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