securities. If subsection (d) or section 4978B(d) applies to a disposition, the disposition shall be treated as made from employer securities in the opposite order of the preceding sentence. . (5) (A) Chapter 43 of such Code is amended by inserting before section 4979 the following new section: 4978B. Tax on disposition of employer securities to which section 133 applied (a) Imposition of tax In the case of an employee stock ownership plan which has acquired section 133 securities, there is hereby imposed a tax on each taxable event in an amount equal to the amount determined under subsection (b). (b) Amount of tax (1) In general The amount of the tax imposed by subsection (a) shall be equal to 10 percent of the amount realized on the disposition to the extent allocable to section 133 securities under section 4978(b)(2). (2) Dispositions other than sales or exchanges For purposes of paragraph (1), in the case of a disposition of employer securities which is not a sale or exchange, the amount realized on such disposition shall be the fair market value of such securities at the time of disposition. (c) Taxable event For purposes of this section, the term taxable event means any of the following dispositions: (1) Dispositions within 3 years Any disposition of any employer securities by an employee stock ownership plan within 3 years after such plan acquired section 133 securities if— (A) the total number of employer securities held by such plan after such disposition is less than the total number of employer securities held after such acquisition, or (B) except to the extent provided in regulations, the value of employer securities held by such plan after the disposition is 50 percent or less of the total value of all employer securities as of the time of the disposition. For purposes of subparagraph (B), the aggregation rule of section 133(b)(6)(D) shall apply. (2) Stock disposed of before allocation Any disposition of section 133 securities to which paragraph (1) does not apply if— (A) such disposition occurs