12 U.S.C. § 626

The directors of any corporation organized under the provisions of this subchapter may, semiannually, declare a dividend of so much of the net profits of the corporation as they shall judge expedient; but each corporation shall, before the declaration of a dividend, carry one-tenth of its net profits of the preceding half year to its surplus fund until the same shall amount to 20 per centum of its capital stock.