26 CFR § 31.3302(a)-3 - Proof of credit under section 3302(a).
Credit against the tax for any calendar year for contributions paid into State unemployment funds shall not be allowed unless there is submitted to the district director:
(a) A certificate of the proper officer of each State (the laws of which required the contributions to be paid) showing, for the taxpayer:
(1) The total amount of contributions required to be paid under the State law with respect to such calendar year (exclusive of penalties and interest) which was actually paid on or before the date the Federal return is required to be filed; and
(2) The amounts and dates of such required payments (exclusive of penalties and interest) actually paid after the date the Federal return is required to be filed.
(b) A statement by the taxpayer that no part of any payment made by him into a State unemployment fund for such calendar year, which is claimed as a credit against the tax, was deducted or is to be deducted from the remuneration of individuals in his employ. Such statement shall contain or be verified by a written declaration that it is made under the penalties of perjury.
(c) Such other or additional proof as the Commissioner or the district director may deem necessary to establish the right to the credit provided for under section 3302(a).
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