Who do I contact when two countries tax the same income?
Each treaty names a body in each country as its competent authority, and that is the office empowered to apply and interpret the agreement and to deal with its counterpart. It is not the same as the office that assessed you, nor the one that hears a domestic objection, and a letter to the wrong part of an administration can sit for a long time. The first step in a double taxation case is therefore to identify, from the treaty text itself, who the competent authority is in each of the two countries, and which of them your case should be presented to.
What is a competent authority in a tax treaty?
It is the body each country designates to operate the treaty: to interpret its terms, to apply them to a case, and to negotiate with the other country's designated body where the two systems produce a result the treaty was meant to prevent. The designation sits in the treaty's definitions article and is usually expressed as an office together with the people it authorises, which is why the practical addressee can be a specialist unit rather than the minister named in the text. Treaty machinery that depends on agreement between two states runs through these two bodies and nowhere else.
Can I write to the competent authority myself?
The treaty route is generally available to the person affected, so a taxpayer can present a case rather than wait for an administration to act. What it requires is a case rather than a complaint: the facts, the article relied on, the treatment in each country, and the double taxation or misapplication that results. The two authorities then deal with each other, and the taxpayer is not a party to that discussion, which is why the material submitted at the outset matters more than it would in an ordinary appeal. Preparing it properly is the work. Sending it is not.
How is this different from filing an objection or appeal?
An objection is a domestic process: you are asking one country to review its own assessment under its own law, and the outcome binds only that country. A treaty case asks the two designated authorities to sort out the interaction between two systems, which is the only route to a result both countries accept. They are not alternatives, and running the treaty route alone can be risky, because domestic time limits keep running while two administrations talk. In many cases the right answer is to protect the domestic position and present the treaty case, keeping the two consistent.
Which country's competent authority should I approach first?
The treaty usually directs the case to the authority of the country the person is resident in, and in some situations to the country whose action caused the problem. Getting this right matters more than it looks, because an authority that should not have received a case may take time to say so, and nothing is advancing meanwhile. Read the relevant article for the routing rule, confirm residence for treaty purposes before relying on it, and where residence is itself the point in dispute, address that in the submission rather than leaving the authority to work it out.
Does a competent authority agreement bind both tax administrations?
An agreement reached between the two authorities is implemented by each of them within its own system, which is what makes it useful: relief given on one side is matched on the other rather than left as a credit nobody will allow. It is not a court judgment, and neither authority is obliged to reach agreement in the first place. There is also usually a step at which the taxpayer has to accept the outcome and, in doing so, give up a parallel domestic challenge on the same point. Understanding that trade-off before the case is presented is part of the preparation.
How would a foreign tax authority know I am resident there?
Mostly from information you or your bank already provided. Account-opening forms ask you to self-certify tax residence, and that certification is reported between authorities under the Common Reporting Standard or, for US accounts, under the FATCA framework. Beyond that: employer and payroll filings, property registries, immigration records and the tax filings of anyone who paid you. The realistic planning assumption is that the data arrives. See FATCA and information reporting.
What is a permanent establishment, and how easily do we create one?
A taxable presence in another country under the treaty — typically a fixed place of business such as an office, branch, factory or workshop, or a dependent agent habitually concluding contracts on your behalf. Some treaties add a services test measured in days. Purely preparatory or auxiliary activity is excluded, but that carve-out is narrower than it sounds: one senior employee working from home in the other country, with authority, has been enough. See business profits and permanent establishment.
