R.I. Gen. Laws § 6-13.1-30: Cash payment for retail purchases.

It shall be a deceptive trade practice in violation of this chapter for any retail establishment offering goods or services for sale to discriminate against a prospective customer by requiring the use of credit for purchase of goods or services. All retail establishments shall accept legal tender currency when offered as payment. Provided, the provisions of this section shall not apply to online purchases or sales made over the internet.