Conn. Gen. Stat. § 12-63c

(b) Any such information related to actual rental and rental-related income and operating expenses and not already a matter of public record that is submitted to the assessor shall not be subject to the provisions of section 1-210 .

(c) If upon receipt of information as required under subsection (a) of this section the assessor finds that such information does not appear to reflect actual rental and rental-related income or operating expenses related to the current use of such property, additional verification concerning such information may be requested by the assessor. All information received by the assessor under subsection (a) of this section shall be subject to audit by the assessor or a designee of the assessor. Any person claiming to be aggrieved by the action of the assessor under this section may appeal the actions of the assessor to the board of assessment appeals and the Superior Court as otherwise provided in this chapter.

(d) (1) Any owner of such real property required to submit information to the assessor in accordance with subsection (a) of this section for any assessment year, who fails to submit such information as required under said subsection (a) or who submits information in incomplete or false form with intent to defraud, shall (A) for assessment years commencing prior to October 1, 2023, be subject to a penalty equal to a ten per cent increase in the assessed value of such property for such assessment year, and (B) for assessment years commencing on or after October 1, 2023, be subject to a penalty equal to a ten per cent increase in the assessed value of such property for such assessment year, which the assessor shall add by issuance of a certificate of correction for failure to file. Upon receipt of any such certificate of correction, the tax collector of the town shall apply the mill rate for the current fiscal year and, if such certificate of correction is received after the normal billing date, not later than thirty days after such receipt, mail or hand deliver a bill to such owner based on the addition of the penalty described in this subdivision. Such tax shall be due and payable and collectible as other municipal taxes and subject to the same liens and processes of collection, provided such tax shall be due and payable in an initial or single installment due and payable not sooner than thirty days after the date prescribed by the tax collector and appearing on such bill, and in any remaining, regular installments, as such installments are due and payable, and the several installments of a tax so due and payable shall be equal.

(2) Notwithstanding the provisions of this subsection, an assessor or board of assessment appeals shall waive such penalty if the owner of the real property required to submit the information is not the owner of such property on the assessment date for the grand list to which such penalty is added. Such assessor or board may waive such penalty upon receipt of such information in any town in which the legislative body adopts an ordinance allowing for such a waiver.
r board of assessment appeals shall waive such penalty if the owner of the real property required to submit the information is not the owner of such property on the assessment date for the grand list to which such penalty is added. Such assessor or board may waive such penalty upon receipt of such information in any town in which the legislative body adopts an ordinance allowing for such a waiver.

(e) Any income and expense disclosure form described in subsection (a) of this section received by the assessor to which such form is due that is in an envelope bearing a postmark, as defined in section 1-2a , showing a date within the allowed filing period, shall not be deemed delinquent.

Cited. 240 C. 192. Municipal tax assessor, in determining present value of real property used primarily to produce rental income, may compel the filing of income and expense reports by property owner in years in which there is no citywide revaluation or interim revaluation of properties in the same class as owner's property, provided there is insufficient sales data as required under Sec. 12-63b. 292 C. 125. The word “submit” unambiguously requires that the income and expense information be received by the assessor by June 1. 345 C. 76.

Subsec. (a):

Legislature's decision not to include the phrase “or postmarked” or other similar language to define “submit” to include mailing is dispositive and in the context of other statutes, all of which appear in title 12 of the General Statutes, the word “submit” is unambiguous and means that the forms must be delivered to the assessor's office by June 1st in order to comply with the statute; Subsec. (d): The ten per cent penalty is not punitive within the meaning of the eighth amendment of the federal constitution and is not subject to the second step of the excessive fines clause analysis, nor is it a “fine” that subjects it to the excessive fines clause of article first, section eight of the Connecticut constitution. 202 CA 467.

Subsec. (d):

Penalty under Subsec. is an “assessment… required by law” within the meaning of Sec. 12-55(b), and as Subsec. contains no express extension of assessor's statutory authority, the deadline for imposing penalties under Subsec. must be the deadline articulated in Sec. 12-55(b), i.e. imposed before assessor signs grand list for applicable assessment year. 339 C. 157.