Both Countries Auditing the Same Income: What Happens and Who Goes First

If you file in both countries, both countries can audit you, and they can do it at the same time. The CRA and the IRS exchange information under Article XXVII of the Canada-US tax treaty, and an audit in one country can trigger an audit in the other. A CRA reassessment that changes your Canadian income changes the foreign tax credit on your US return. An IRS adjustment that reclassifies income changes what you report to the CRA. The two files are connected, and the responses need to be coordinated. This page covers how the information exchange works, what happens when both countries audit the same income, and how to avoid making one audit worse by mishandling the other.

How does information exchange trigger a second audit?

Article XXVII authorizes the CRA and IRS to exchange information “as is relevant for carrying out the provisions of this Convention or of the domestic laws” of both countries. The exchange is broad and includes:

Automatic exchange. Under FATCA (the Foreign Account Tax Compliance Act) and the intergovernmental agreement between Canada and the US, Canadian financial institutions report US-person account information to the CRA, which transmits it to the IRS. The IRS reciprocates with information about Canadian-person accounts at US financial institutions. This automatic exchange covers account balances, interest, dividends, and gross proceeds.

Spontaneous exchange. If the CRA audits a Canadian taxpayer and discovers information relevant to a US filing (unreported US income, incorrect treaty claims, foreign tax credit inconsistencies), the CRA may spontaneously share that information with the IRS, even without a specific request. The IRS does the same in reverse.

Specific request. Either country can request specific information about a taxpayer from the other. If the IRS is auditing a US person’s foreign tax credit and needs the Canadian return or the CRA’s assessment details, it can request them through the treaty exchange mechanism.

The practical effect: an audit in one country is not isolated. The CRA auditor who adjusts your Canadian rental income will note the cross-border dimension, and that information may reach the IRS through spontaneous exchange. The IRS examiner who disallows your foreign tax credit may request your Canadian return through the treaty. Each audit feeds the other.

Which country’s outcome controls?

Neither country’s outcome automatically controls the other. Each country applies its own tax law to the income, and each audit produces its own assessment. But the outcomes are connected through three mechanisms:

Foreign tax credits. If the CRA increases your Canadian tax on a particular item of income, your US foreign tax credit for that income increases. If the IRS disallows a foreign tax credit, the US tax on that income increases. Any change in one country’s tax directly affects the credit calculation in the other.

Treaty claims. If one country reclassifies income (for example, the IRS treats a payment as a royalty instead of a service fee), the treaty article that governs the income may change, which affects the other country’s taxing right.

Income allocation. If one country increases income (the CRA adds unreported Canadian-source income), the other country’s allocation of the same income may need to change. The US return reports worldwide income, so Canadian income is already included; the question is whether the amounts match and whether the treaty allocation is correct.

The coordination problem: if you concede an issue in one country (accepting a CRA reassessment), the concession affects your position in the other country. If you accept that the CRA is correct that you earned $50,000 more in Canadian business income, your US return needs to report that income too (it should already be there as part of worldwide income, but the amounts, timing, and character must match). Conversely, if you successfully dispute the CRA’s reassessment, the basis for any IRS adjustment based on the same facts is weakened.

How do I coordinate responses?

Do not take contradictory positions. If you tell the CRA that your departure date was October 15, 2023, and you tell the IRS that your departure date was March 1, 2024, both countries will notice. The treaty exchange makes contradictory positions visible, and either country can use the inconsistency against you.

Align the facts. Before responding to either audit, reconcile the underlying facts across both returns. The income amounts, the dates, the characterization of payments, and the treaty positions should be consistent. If the CRA and IRS are asking about different aspects of the same transaction, your answers should fit together.

Decide which audit to resolve first. If possible, resolve the audit in the country that initiated the action first. If the CRA reassessed you and the IRS is asking follow-up questions based on information received from the CRA, resolving the CRA dispute first establishes the baseline that the US return can adjust to. If the IRS initiated the action (adjusting the US return, which then affected the Canadian foreign tax credit), resolve the US side first.

File protective claims. When one country changes the tax, file a protective claim in the other country to preserve your ability to adjust. In Canada, this means filing a T1-ADJ (adjustment request) or, if the reassessment period is closing, a notice of objection. In the US, this means filing an amended return (Form 1040-X) or a protective refund claim on Form 843 within the refund statute of limitations (IRC 6511).

Consider representation in both countries. A practitioner licensed in both jurisdictions can coordinate the responses and ensure consistency. A Canadian-only accountant responding to the CRA audit may not realize that a concession on Canadian business income affects the US foreign tax credit. A US-only preparer responding to the IRS may not understand the CRA’s departure tax provisions. The cross-border angle is where representation pays for itself.

What about simultaneous examination programs?

The CRA and IRS have the authority to conduct simultaneous examinations of the same taxpayer under a bilateral agreement. In a simultaneous examination, auditors from both countries coordinate their work, share findings in real time, and work toward a consistent outcome. The taxpayer is notified that the examination is simultaneous.

Simultaneous examinations are more common for large corporations with significant cross-border transactions (transfer pricing, intercompany financing, cost-sharing arrangements). They are less common for individuals, but they do occur, particularly for high-net-worth individuals with complex cross-border structures or for taxpayers under investigation for potential non-compliance in both countries.

In a simultaneous examination, the coordination problem is handled by the auditors themselves. The taxpayer’s role is to respond to each country’s requests and to ensure consistency in the information provided. Having a single representative who communicates with both audit teams is particularly valuable here.

When does double taxation survive both audits?

Even after both countries complete their audits, double taxation can persist if:

• One country increases income and the other does not make a corresponding adjustment.
• Both countries claim taxing rights on the same income under different treaty articles.
• The foreign tax credit in one country does not fully offset the tax in the other (because of credit limitations, timing differences, or characterization mismatches).

When double taxation survives the normal processes, the Competent Authority / Mutual Agreement Procedure under Article XXVI is the mechanism for resolution. The competent authorities of both countries negotiate to eliminate the double taxation. This is a government-to-government process, free to the taxpayer, with a mandatory arbitration backstop under the 2007 protocol if the competent authorities cannot agree within two years.

What should I do next?

If you are being audited by one country, check whether the other country has also contacted you or is likely to. Reconcile the facts across both returns before responding to either. File protective claims in the other country to preserve your rights. Do not take contradictory positions. If both countries have completed their audits and double taxation remains, file a Competent Authority request.

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.