Objections and Appeals in Ontario
Reviewed by the Commoner Law Editorial Team. Sourced from Canadian federal statutes and official sources. Provincial information reflects each province's own legislation and court rulings. Written in plain language for general understanding — this is educational content, not legal advice. Our editorial standards
What is this right?
If you disagree with a CRA assessment or reassessment, you can file a Notice of Objection under Section 165 of the Income Tax Act.
For individuals, the deadline is the later of 90 days from the date of assessment or one year after the filing deadline for that tax year. For corporations, the deadline is 90 days only.
Once you file, a CRA Appeals officer reviews your case independently from the auditor who made the original decision. This is a fresh look at your situation.
If you are still unsatisfied after the Appeals review, you can appeal to the Tax Court of Canada within 90 days of the CRA's decision. The Informal Procedure is available for disputes under $25,000 — it is simpler, faster, and you do not need a lawyer.
If the CRA has not responded to your objection within 90 days, you can go directly to Tax Court without waiting (Section 169).
When does it apply?
This applies to any taxpayer who has received a Notice of Assessment or Reassessment they disagree with.
- Individuals have the later of 90 days or one year after the filing deadline.
- Corporations have 90 days only.
- Late-filed objections may be accepted if you apply within one additional year under Section 166.1.
What to Do If You Disagree with a CRA Tax Assessment in Canada
- Act quickly — mark the 90-day deadline on your calendar as soon as you get your assessment.
- File Form T400A online through My Account or by mail.
- Clearly state the issues, relevant facts, and legal basis for your disagreement.
- Wait for the Appeals officer's review — they will contact you to discuss.
- If still unsatisfied, file with the Tax Court of Canada within 90 days of the CRA's decision.
- If CRA has not responded within 90 days, you can go directly to Tax Court.
What should you NOT do?
- Don't miss the 90-day deadline — this is the most common and costly mistake taxpayers make.
- Don't assume filing an objection means you don't have to pay — individuals get a postponement of collection, but large corporations must pay 50% upfront.
- Don't file a vague objection — clearly explain what you disagree with and why.
- Don't confuse a service complaint with a formal objection — they are different processes with different outcomes.
How Ontario differs from federal law
If you disagree with a CRA assessment of your federal and Ontario income tax, you follow the federal objection and appeal process. Ontario does not have a separate tax appeals body for income tax.
- File a Notice of Objection within 90 days of receiving your Notice of Assessment or Reassessment. You can file online through My Account or by mail using CRA Form T400A.
- The CRA Appeals Division will review your objection. They operate independently from the auditors who made the original assessment.
- If the objection is denied, you can appeal to the Tax Court of Canada. The Tax Court has offices in Toronto and holds sittings across Ontario. You can choose the informal procedure (for amounts under $25,000 in federal tax or $50,000 in combined tax and penalties) — no lawyer is needed and the process is simpler.
- Further appeals go to the Federal Court of Appeal and, with leave, to the Supreme Court of Canada.
- For Ontario property tax assessments (municipal property tax), you appeal to the Assessment Review Board (ARB) if you disagree with your MPAC property assessment. The deadline is usually March 31 of the tax year.
Additional Steps in Ontario
File your Notice of Objection promptly — the 90-day deadline is strict, though late-filing relief is available within one year in some circumstances. For property assessment appeals, contact MPAC (mpac.ca) to request a reconsideration before filing a formal appeal with the Assessment Review Board. Community Legal Clinics and tax clinics can help with tax objections for low-income Ontarians.
Relevant Law: Income Tax Act, R.S.C. 1985, c. 1 (5th Supp.), ss. 165–169 (Objections and Appeals); Tax Court of Canada Act, R.S.C. 1985, c. T-2; Assessment Act, R.S.O. 1990, c. A.31 (property assessment appeals)
Common Questions
When does objections and appeals apply?
This applies to any taxpayer who has received a Notice of Assessment or Reassessment they disagree with.Individuals have the later of 90 days or one year after the filing deadline.Corporations have 90 days only.Late-filed objections may be accepted if you apply within one additional year under Section 166.1.
What should I do if the CRA assessed me incorrectly and I want to dispute it in Canada?
Act quickly — mark the 90-day deadline on your calendar as soon as you get your assessment.File Form T400A online through My Account or by mail.Clearly state the issues, relevant facts, and legal basis for your disagreement.Wait for the Appeals officer's review — they will contact you to discuss.If still unsatisfied, file with the Tax Court of Canada within 90 days of the CRA's decision.If CRA has not responded within 90 days, you can go directly to Tax Court.
What mistakes should I avoid with objections and appeals?
Don't miss the 90-day deadline — this is the most common and costly mistake taxpayers make.Don't assume filing an objection means you don't have to pay — individuals get a postponement of collection, but large corporations must pay 50% upfront.Don't file a vague objection — clearly explain what you disagree with and why.Don't confuse a service complaint with a formal objection — they are different processes with different outcomes.
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