R.I. Gen. Laws § 28-43-5.1
Any employer who has been assigned an experience rate, and who has filed all reports required under chapters 42 - 44 of this title, and has paid all contributions, interest, and penalties due under chapters 42 - 44 of this title, may make a voluntary contribution to his or her account. Such voluntary contribution shall be paid not later than thirty (30) days after the date on which the department has issued a notice of the employer's experience rate, or prior to the expiration of one-hundred-twenty (120) days after the start of the calendar year, for which the experience rate is effective, whichever is earlier. Upon timely payment of a voluntary contribution, the contribution shall be credited to the employer's account balance and that employer shall receive a recomputation of its experience rate for that calendar year. No voluntary contribution shall be refunded in whole or in part.
R.I. Gen. Laws § 28-43-5.1