Code of Federal Regulations Title 26. Internal Revenue § 26.31.3302(b)–2 Proof of additional credit under section 3302(b)

(a) To the Commissioner a certificate of the proper officer of each State (with respect to the law of which the additional credit is claimed) showing the highest rate of contributions applied under the State law in such calendar year to any person having individuals in his employ;  and

(b) To the district director a certificate of the proper officer of each State (with respect to the law of which the additional credit is claimed) showing for the taxpayer—

If under the law of such State different rates of contributions were applied to the taxpayer during particular periods of such calendar year, the certificate shall set forth the information called for in paragraphs (b)(1) and (2) of this section with respect to each such period.

(c) Such other or additional proof as the Commissioner or the district director may deem necessary to establish the right to the additional credit provided for under section 3302(b).