of credit to patrons of agricultural cooperative (A) Election to allocate (i) In general In the case of an eligible cooperative organization, any portion of the credit determined under subsection (a) for the taxable year may, at the election of the organization, be apportioned among patrons of the organization on the basis of the amount of business done by the patrons during the taxable year. (ii) Form and effect of election An election under clause (i) for any taxable year shall be made on a timely filed return for such year. Such election, once made, shall be irrevocable for such taxable year. Such election shall not take effect unless the organization designates the apportionment as such in a written notice mailed to its patrons during the payment period described in section 1382(d). (B) Treatment of organizations and patrons The amount of the credit apportioned to any patrons under subparagraph (A)— (i) shall not be included in the amount determined under subsection (a) with respect to the organization for the taxable year, and (ii) shall be included in the amount determined under subsection (a) for the first taxable year of each patron ending on or after the last day of the payment period (as defined in section 1382(d)) for the taxable year of the organization or, if earlier, for the taxable year of each patron ending on or after the date on which the patron receives notice from the cooperative of the apportionment. (C) Special rules for decrease in credits for taxable year If the amount of the credit of a cooperative organization determined under subsection (a) for a taxable year is less than the amount of such credit shown on the return of the cooperative organization for such year, an amount equal to the excess of— (i) such reduction, over (ii) the amount not apportioned to such patrons under subparagraph (A) for the taxable year, shall be treated as an increase in tax imposed by this chapter on the organization. Such increase shall not be treated as tax imposed by this chapter for purposes of