26 CFR § 1.537-3 - Business of the corporation.
(a) The business of a corporation is not merely that which it has previously carried on but includes, in general, any line of business which it may undertake.
(b) If one corporation owns the stock of another corporation and, in effect, operates the other corporation, the business of the latter corporation may be considered in substance, although not in legal form, the business of the first corporation. However, investment by a corporation of its earnings and profits in stock and securities of another corporation is not, of itself, to be regarded as employment of the earnings and profits in its business. Earnings and profits of the first corporation put into the second corporation through the purchase of stock or securities or otherwise, may, if a subsidiary relationship is established, constitute employment of the earnings and profits in its own business. Thus, the business of one corporation may be regarded as including the business of another corporation if such other corporation is a mere instrumentality of the first corporation; that may be established by showing that the first corporation owns at least 80 percent of the voting stock of the second corporation. If the taxpayer's ownership of stock is less than 80 percent in the other corporation, the determination of whether the funds are employed in a business operated by the taxpayer will depend upon the particular circumstances of the case. Moreover, the business of one corporation does not include the business of another corporation if such other corporation is a personal holding company, an investment company, or a corporation not engaged in the active conduct of a trade or business.
The following state regulations pages link to this page.