Carter Co. (a C Corp.), who is a calendar year taxpayer received a check for $180,000 in payment for services rendered as a commissioned sales agent near the end of 2017.

In 2018, the customer discovered that the commission was incorrectly calculated on the sale, and Carter Co. refunded $30,000 of the $180,000 to the customer.

Carter Co. was in a 35% tax bracket in 2017, but in 2018 due to the Tax Cuts and Jobs Act is now in a 21% bracket. Since Carter Co. was taxed on the full $180,000 under the claim of right doctrine, it may deduct the $30,000 in 2018, but this will not "make them whole."

What authority would provide Carter Co. relief? What is the statutory authority? Regulatory authority?