26 USC 6676 - Erroneous claim for refund or credit

(a) Civil penalty 
If a claim for refund or credit with respect to income tax (other than a claim for a refund or credit relating to the earned income credit under section 32) is made for an excessive amount, unless it is shown that the claim for such excessive amount has a reasonable basis, the person making such claim shall be liable for a penalty in an amount equal to 20 percent of the excessive amount.
(b) Excessive amount 
For purposes of this section, the term excessive amount means in the case of any person the amount by which the amount of the claim for refund or credit for any taxable year exceeds the amount of such claim allowable under this title for such taxable year.
(c) Coordination with other penalties 
This section shall not apply to any portion of the excessive amount of a claim for refund or credit which is subject to a penalty imposed under part II of subchapter A of chapter 68.