Example 1. A syndicate which maintains its headquarters in a foreign country has representatives in the United States who receive wagers in the United States for or on behalf of such syndicate. For the purposes of section 4404, such wagers are considered as accepted within the United States, the syndicate is considered to be in the business of accepting wagers within the United States, and such wagers are subject to the tax. This is true regardless of the nationality or residence of the members of the syndicate.
Example 2. A Canadian citizen employed in Detroit, Michigan, telephones a horse race bet to a bookmaker who is a United States citizen with his place of business located in Windsor, Canada. The wager is taxable since it is made by a person within the United States with a person who is a United States citizen.
Example 3. A United States citizen while visiting Tijuana, Mexico, makes a wager on the outcome of a horse race with a bookmaker who is also a United States citizen located and doing business in Tijuana. The wager is not taxable since both parties to the wager, though United States citizens, were outside the United States at the time the wager was made.
26 C.F.R. §44.4404-1