Objections and Appeals — Ontario
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 an assessment or reassessment, you can file a Notice of Objection under section 165. This is the formal first step — and the one most people miss because the deadline is short.
For individuals, you have the later of 90 days from the assessment date or one year after the return's filing due date. For corporations, it's 90 days only. The Act does not extend these clocks generously.
Once filed, the case moves to a CRA Appeals officer who reviews it independently from the auditor who made the original decision. That separation matters — it's the first time fresh eyes look at your file.
Still unsatisfied? Appeal to the Tax Court of Canada within 90 days of the Appeals decision. For disputes under $25,000, the Informal Procedure is the way: simpler rules, faster timelines, no lawyer required.
And if the CRA goes silent for 90 days after your objection, you can skip the wait and head straight to Tax Court under section 169.
When does it apply?
Applies to any taxpayer who's received a Notice of Assessment or Reassessment they disagree with.
- Individuals: the later of 90 days or one year after the filing deadline.
- Corporations: 90 days, period.
- A late-filed objection can sometimes be accepted within one additional year under s. 166.1, but only if you can explain the delay.
What to Do If You Disagree with a CRA Tax Assessment in Canada
- Mark the 90-day deadline the moment the assessment lands.
- File Form T400A through My Account or by mail.
- Lay out the issues, the relevant facts, and the legal basis — vague objections drift.
- Wait for the Appeals officer to make contact. They will.
- If you still disagree, file with the Tax Court of Canada within 90 days of the decision.
- If CRA hasn't responded after 90 days, go straight to Tax Court — you don't have to wait.
What should you NOT do?
- Don't miss the 90-day deadline. The most common and costliest mistake in Canadian tax practice.
- Don't assume objection equals no payment. Individuals get collection postponed, but large corporations have to pay 50% upfront.
- Don't file vague objections. Spell out what you disagree with and why.
- Don't confuse a service complaint with a formal objection. Different processes, different outcomes — the service complaint route doesn't preserve appeal rights.
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
What is the objections and appeals right in Canada?
If you disagree with an assessment or reassessment, you can file a Notice of Objection under section 165. This is the formal first step — and the one most people miss because the deadline is short.For individuals, you have the later of 90 days from the assessment date or one year after the return's filing due date. For corporations, it's 90 days only. The Act does not extend these clocks generously.Once filed, the case moves to a CRA Appeals officer who reviews it independently from the auditor who made the original decision. That separation matters — it's the first time fresh eyes look at you...
When does objections and appeals apply?
Applies to any taxpayer who's received a Notice of Assessment or Reassessment they disagree with.Individuals: the later of 90 days or one year after the filing deadline.Corporations: 90 days, period.A late-filed objection can sometimes be accepted within one additional year under s. 166.1, but only if you can explain the delay.
What should I do if the CRA assessed me incorrectly and I want to dispute it in Canada?
Mark the 90-day deadline the moment the assessment lands.File Form T400A through My Account or by mail.Lay out the issues, the relevant facts, and the legal basis — vague objections drift.Wait for the Appeals officer to make contact. They will.If you still disagree, file with the Tax Court of Canada within 90 days of the decision.If CRA hasn't responded after 90 days, go straight to Tax Court — you don't have to wait.
What mistakes should I avoid with objections and appeals?
Don't miss the 90-day deadline. The most common and costliest mistake in Canadian tax practice.Don't assume objection equals no payment. Individuals get collection postponed, but large corporations have to pay 50% upfront.Don't file vague objections. Spell out what you disagree with and why.Don't confuse a service complaint with a formal objection. Different processes, different outcomes — the service complaint route doesn't preserve appeal rights.
Objections and Appeals in other states
Same topic, different jurisdiction. Pick the one that applies to you.