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 Collector of Internal Revenue; 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.