26 CFR § 44.4404-1 - Territorial extent.
(a) In general. The tax imposed by section 4401 applies to wagers (1) accepted in the United States, or (2) placed by a person who is in the United States (i) with a person who is a citizen or resident of the United States, or (ii) in a wagering pool or lottery conducted by a person who is a citizen or resident of the United States. All wagers made within the United States are taxable irrespective of the citizenship or place of residence of the parties to the wager. Thus, the tax applies to wagers placed within the United States, even though the person for whom or on whose behalf the wagers are received is located in a foreign country and is not a citizen or resident of the United States. Likewise, a wager accepted outside the United States by a citizen or resident of the United States is taxable if the person making such wager is within the United States at the time the wager is made.
(b) Examples. The following examples illustrate the application of paragraph (a) of this section: