(a) Any company which, either intentionally or through error, fails to include in its return items of income or invested capital or which claims unlawful deductions therefrom shall make a supplemental return disclosing such facts within three years from the due date of the return and, within thirty days thereafter, shall pay to the commissioner any tax due thereon, with interest upon the amount of such additional tax at the rate of one per cent per month or fraction thereof from the date when the original tax became due and payable.

Terms Used In Connecticut General Statutes 12-225

(b) (1) Any company which fails to include in its return items of deductions or includes items of nontaxable income or makes any other error in such return may, within three years from the due date of the return, file with the commissioner an amended return, together with a claim for refund of taxes overpaid as shown by such amended return. Failure to file a claim within the time prescribed in this section constitutes a waiver of any demand against the state on account of overpayment. The commissioner shall, within one hundred eighty days of the receipt of such claim, determine whether such claim is valid and, if so, the commissioner shall notify the State Comptroller of the amount of such refund and the State Comptroller shall draw an order on the State Treasurer in the amount thereof for payment to such company. If the commissioner determines that such claim is not valid, either in whole or in part, he shall mail notice of the proposed disallowance in whole or in part of the claim to the company which notice shall set forth briefly the commissioner’s findings of fact and the basis of disallowance in each case decided in whole or in part adversely to the claimant. Sixty days after the date on which it is mailed, a notice of proposed disallowance shall constitute a final disallowance except only for such amount as to which the company has filed, as provided in subdivision (2) of this subsection, a written protest with the commissioner. For the purposes of computing any refund due or adjusting net income as a result of the inclusion of income, the taxation of which by the state of Connecticut is prohibited by federal law, including the Constitution of the United States, as applied, no expenses related to such income shall be deducted in computing net income under this chapter.

(2) On or before the sixtieth day after the mailing of the proposed disallowance, the company may file with the commissioner a written protest against the proposed disallowance in which it sets forth the grounds on which the protest is based. If a protest is filed, the commissioner shall reconsider the proposed disallowance and, if the company has so requested, may grant or deny the company or its authorized representatives an oral hearing.

(3) The commissioner shall mail notice of his determination to the company, which notice shall set forth briefly the commissioner’s findings of fact and the basis of decision in each case decided in whole or in part adversely to the company.

(4) The action of the commissioner on the company’s protest shall be final upon the expiration of one month from the date on which he mails notice of his action to the company unless within such period the company seeks judicial review of the commissioner’s determination pursuant to § 12-237.