If the CRA believes you owe more tax it will send you a Notice of Reassessment. It is very important that you file a Notice of Objection on time and to the right office (if you disagree about owing the tax). More importantly, the Notice of Objection must deal with all of the legal and factual issues that the CRA has raised. A successful objection must also canvas the legal principles that you can rely on that the CRA did not raise. Drache Aptowitzer LLP lawyers may be able to help you if miss the deadline and draft a submission to convince the CRA to drop the assessment or otherwise reduce the amount owing.