26 CFR 513.6 - Pensions and life annuities.
(a) Pensions, other than pensions paid by the Government of the United States to individuals in respect of services rendered thereto in the discharge of governmental functions, and any life annuity, derived from sources within the United States in taxable years beginning on or after January 1, 1951, by a nonresident alien individual who is resident in Ireland for the purposes of Irish tax are exempt from United States tax under the provisions of Article XII of the convention.
(b) To obviate withholding at the source in the case of such exempt income the nonresident alien individual who is resident in Ireland for the purposes of Irish tax shall notify the withholding agent by letter in duplicate that such income is exempt from United States tax under the provisions of Article XII of the convention. The letter of notification shall be signed by the owner of the income, shall show the name and address of both the payer and the owner, and shall contain a statement that the owner, an individual, is neither a citizen nor a resident of the United States but is resident in Ireland for the purposes of Irish tax. This letter shall constitute authorization for the payment of such income without deduction of the tax at source unless the Commissioner of Internal Revenue subsequently notifies the withholding agent that the tax should be withheld from payments of such income made after receipt of such notice. If, after filing a letter of notification, the owner of the income ceases to be eligible for the benefit of the convention, he must promptly notify the withholding agent by letter in duplicate.