Conn. Gen. Stat. § 12-581
Each person subject to a tax imposed under section 12-579, shall file a return on or before the twentieth of each month setting forth the amount of tax due for the preceding month and such additional information as the tax collector may require. Payment of the tax shall accompany such return. Any person subject to such tax failing to file a return and pay the tax when due is liable for a penalty of ten dollars or ten per cent of the tax due, whichever is greater. In addition, there shall be added interest at the rate of one and one-half per cent per month, or fraction thereof, from the date of the return until date of payment. The tax collector, if satisfied that the failure to comply with any provision of this section was due to reasonable cause, may abate or remit the whole or part of any penalty.
Conn. Gen. Stat. § 12-581
(P.A. 74-308, S. 3; P.A. 82-163, S. 4, 6.)