Can a country's own law override a tax treaty?
In some countries it can. Whether domestic legislation is capable of displacing a treaty provision depends on that country's constitutional arrangements. In some systems a treaty sits above ordinary legislation; in others a later statute can prevail over it. So the question has no single answer and has to be asked of the specific country whose return you are filing. The practical consequence is that reading the treaty article is not the end of the analysis. You also need to know what the domestic law of each country did with that article in the year concerned.
How do I know if domestic law has overridden the article I rely on?
By reading the domestic provision that charges the income alongside the treaty article, rather than reading the treaty alone. Overrides are rarely labelled as such. They appear as ordinary charging or deeming provisions whose effect is to tax something the treaty had allocated elsewhere, or to refuse a relief the treaty made available. Two questions identify them. Does the domestic rule reach the income the article dealt with, and does it say anything about how it interacts with agreements? Where the answer to the first is yes and the second is silent, the position depends on that country's hierarchy of law.
Does a treaty always beat a country's domestic tax law?
No, and assuming it does is how a position gets built on the wrong foundation. Many countries do give treaties priority, and there the treaty resolves the conflict. Others allow a later domestic enactment to take effect regardless. There is also a middle case, more common than outright conflict: a domestic rule that does not contradict the treaty but changes the result it would otherwise produce, for instance by re-characterising a payment before the treaty is applied. In all three situations the answer comes from the governing texts of the country in question, not from the general principle.
What happens to my treaty claim if the law changed during the year?
You may have two positions for one year. Where a domestic provision that displaces or alters a treaty outcome takes effect part way through, income arising before and after that date can be treated differently, and the effective-date wording decides which. Check whether the provision applies by reference to when the income arose, when it was paid, or to accounting periods beginning after a date, because those give different splits. The practical work is a schedule of the income by date with the applicable basis against each part, rather than one claim covering the whole year.
Is an anti-abuse or purpose test the same as a treaty override?
No, and the difference decides which argument you run. A purpose or eligibility test inside the treaty is the treaty's own condition: the benefit was never available unless the test is met, and the answer comes from the article itself. An override is domestic law displacing what the treaty allocated. Argue the constitutional hierarchy when the real obstacle is a test in the agreement, and you have answered a question nobody asked. So the first step is to locate where the obstacle sits, in the agreement or in the statute, before deciding what has to be proved.
Who decides when a treaty and a statute conflict?
Ultimately the courts of the country applying its own law, on its own constitutional rules. That is not much comfort when a return is due, so in practice the position is taken on the governing texts and the available authority, and the file records the reasoning and the alternative. The other country's view does not resolve it either. Each authority applies its own hierarchy, which is exactly how the same income ends up taxed in both places despite an agreement. Where the exposure is significant, the mechanism a treaty provides for the two authorities to settle it is worth considering early.
How do Canadians reduce US estate tax exposure?
The treaty does much of the work: it gives a Canadian resident a credit pro-rated by the share of the worldwide estate made up of US assets, plus a marital credit that can defer exposure on a transfer to a spouse. Beyond that the levers are the ones you would expect — the domicile of the funds you hold, whether US real property is held directly or through a structure, and life insurance to fund the liability rather than reduce it. Worldwide estate value is what the pro-ration turns on. See treaty relief on US estate tax.
What is double tax relief and how is it given?
Three mechanisms, and which one you get depends on your residence country's law and the treaty. Exemption leaves the foreign income out of the residence-country base. Credit taxes it and then subtracts the foreign tax, capped at the residence-country tax on that income. Deduction merely reduces taxable income by the foreign tax, and is usually the weakest. Canada and the United States lead with credit; several treaties give exemption for specific income types. See claiming the credit.
