Conn. Gen. Stat. § 12-39h: Application of partial payment toward state tax liability in penalties, tax and interest.

Notwithstanding any instructions by the payor to the contrary, any partial payment against any tax outstanding shall be applied by the Commissioner of Revenue Services first to any penalties unless a waiver of penalty has been requested and approved in accordance with the general statutes, and (1) for periods ending on or after July 1, 2018, and prior to December 31, 2019, any amount in excess of such penalty shall be applied first to such tax and then to the interest on such tax, and (2) for periods ending on and after December 31, 2019, any amount in excess of such penalty shall be applied first to interest on such tax and then to the tax.