26 U.S. Code § 307 - Basis of stock and stock rights acquired in distributions
If a shareholder in a corporation receives its stock or rights to acquire its stock (referred to in this subsection as “new stock”) in a distribution to which section 305(a) applies, then the basis of such new stock and of the stock with respect to which it is distributed (referred to in this section as “old stock”), respectively, shall, in the shareholder’s hands, be determined by allocating between the old stock and the new stock the adjusted basis of the old stock. Such allocation shall be made under regulations prescribed by the Secretary.
The election referred to in paragraph (1) shall be made in the return filed within the time prescribed by law (including extensions thereof) for the taxable year in which such rights were received. Such election shall be made in such manner as the Secretary may by regulations prescribe, and shall be irrevocable when made.
For basis of stock and stock rights distributed before June 22, 1954, see section 1052.