Norse Co, an 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 computed on the sale, and Norse Inc. refunded $30,000of the $180,000 to the customer.

Norse Inc. (a C corporation) 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 in 2018. Since Norse 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."

Identify the authority which would provide them relief.

What is the primary authority, regulatory authority, and statutory authority?