— Recovery of tax erroneously or illegally collected.
Section 306
SEC. 306. — Recovery of tax erroneously or illegally collected. — No suit or proceeding shall be maintained in any court for the recovery of any national internal revenue tax hereafter alleged to have been erroneously or illegally assessed or collected, or of any penalty claimed to have been collected without authority, or of any sum alleged to have been excessive or in any manner wrongfully collected, until a claim for refund or credit has been duly filed with the Commissioner; but such suit or proceeding may be maintained, whether or not such tax penalty, or sum has been paid under protest or duress. In any case, no such suit or proceeding shall be begun after the expiration of two years from the date of payment of the tax or penalty regardless of any supervening cause that may arise after payment: Provided, however, That the Commissioner may, even without a written claim therefor, refund or credit any tax, where on the face of the return upon which payment was made, such payment appears clearly to have been erroneously paid.