26 U.S.C. § 384: Limitation on use of preacquisition losses to offset built-in gains

a corporation acquires directly (or through 1 or more other corporations) control of another corporation, or the assets of a corporation are acquired by another corporation in a reorganization described in subparagraph (A), (C), or (D) of section 368(a)(1), and either of such corporations is a gain corporation, Subsection (a) shall not apply to the preacquisition loss of any corporation if such corporation and the gain corporation were members of the same controlled group at all times during the 5-year period ending on the acquisition date. “more than 50 percent” shall be substituted for “at least 80 percent” each place it appears, the ownership requirements of section 1563(a) must be met both with respect to voting power and value, and the determination shall be made without regard to subsection (a)(4) of section 1563. If either of the corporations referred to in paragraph (1) was not in existence throughout the 5-year period referred to in paragraph (1), the period during which such corporation was in existence (or if both, the shorter of such periods) shall be substituted for such 5-year period. such asset was not held by the gain corporation on the acquisition date, or the fair market value of such asset on the acquisition date, over the adjusted basis of such asset on such date. Any item of income which is properly taken into account for any recognition period taxable year but which is attributable to periods before the acquisition date shall be treated as a recognized built-in gain for the taxable year in which it is properly taken into account and shall be taken into account in determining the amount of the net unrealized built-in gain. the net unrealized built-in gain, reduced by the recognized built-in gains for prior years ending in the recognition period which (but for this section) would have been offset by preacquisition losses. in any case described in subsection (a)(1)(A), the date on which the acquisition of control occurs, or in any case described in subsection (a)(1)(B), the date of the transfer in the reorganization. any net operating loss carryforward to the taxable year in which the acquisition date occurs, and any net operating loss for the taxable year in which the acquisition date occurs to the extent such loss is allocable to the period in such year on or before the acquisition date. In the case of a corporation with a net unrealized built-in loss, the term “preacquisition loss” includes any recognized built-in loss. The term “gain corporation” means any corporation with a net unrealized built-in gain. The term “control” means ownership of stock in a corporation which meets the requirements of section 1504(a)(2). Except as provided in regulations and except for purposes of subsection (b), all corporations which are members of the same affiliated group immediately before the acquisition date shall be treated as 1 corporation. To the extent provided in regulations, section 1504 shall be applied without regard to subsection (b) thereof for purposes of the preceding sentence. Any reference in this section to a corporation shall include a reference to any predecessor or successor thereof. Except as provided in regulations, the terms “net unrealized built-in gain”, “net unrealized built-in loss”, “recognized built-in loss”, “recognition period”, and “recognition period taxable year”, have the same respective meanings as when used in section 382(h), except that the acquisition date shall be taken into account in lieu of the change date. Rules similar to the rules of subsection (a) shall also apply in the case of any excess credit (as defined in section 383(a)(2)) or net capital loss. If any preacquisition loss may not offset a recognized built-in gain by reason of this section, such gain shall not be taken into account in determining under section 172(b)(2) the amount of such loss which may be carried to other taxable years. A similar rule shall apply in the case of any excess credit or net capital loss limited by reason of subsection (d). a preacquisition loss for any taxable year is subject to limitation under subsection (a), and a net operating loss from such taxable year is not subject to such limitation, the use of any provision of law or regulations (including subchapter K of this chapter), or contributions of property to a corporation. a binding written contract in effect on or before December 15, 1987 , or a letter of intent or agreement of merger signed on or before December 15, 1987 .”