26 U.S.C. § 1443: Foreign tax-exempt organizations

(a) Income subject to section 511In the case of income of a foreign organization subject to the tax imposed by section 511, this chapter shall apply to income includible under section 512 in computing its unrelated business taxable income, but only to the extent and subject to such conditions as may be provided under regulations prescribed by the Secretary. (b) Income subject to section 4948In the case of income of a foreign organization subject to the tax imposed by section 4948(a), this chapter shall apply, except that the deduction and withholding shall be at the rate of 4 percent and shall be subject to such conditions as may be provided under regulations prescribed by the Secretary.