26 U.S.C. § 887: Imposition of tax on gross transportation income of nonresident aliens and foreign corporations

In the case of any nonresident alien individual or foreign corporation, there is hereby imposed for each taxable year a tax equal to 4 percent of such individual’s or corporation’s United States source gross transportation income for such taxable year. Except as provided in paragraphs (2) and (3), the term “United States source gross transportation income” means any gross income which is transportation income (as defined in section 863(c)(3)) to the extent such income is treated as from sources in the United States under section 863(c)(2). To the extent provided in regulations, such term does not include any income of a kind to which an exemption under paragraph (1) or (2) of section 883(a) would not apply. The term “United States source gross transportation income” shall not include any income taxable under section 871(b) or 882. The term “United States source gross transportation income” does not include any income taxable in a possession of the United States under the provisions of this title as made applicable in such possession. the taxpayer has a fixed place of business in the United States involved in the earning of United States source gross transportation income, and substantially all of the United States source gross transportation income (determined without regard to paragraph (2)) of the taxpayer is attributable to regularly scheduled transportation (or, in the case of income from the leasing of a vessel or aircraft, is attributable to a fixed place of business in the United States). Any income taxable under this section shall not be taxable under section 871, 881, or 882.