used in a separate unit of a trade or business of a predecessor, and immediately after the acquisition employs in his trade or business an individual who immediately prior to the acquisition was employed in the trade or business of such predecessor, then, for the purpose of determining whether the successor employer has paid remuneration with respect to employment equal to the contribution and benefit base (as determined under section 230 of the Social Security Act) to such individual during such calendar year, any remuneration with respect to employment paid (or considered under this paragraph as having been paid) to such individual by such predecessor during such calendar year and prior to such acquisition shall be considered as having been paid by such successor employer. (3) Remuneration For purposes of this subsection, the term remuneration does not include remuneration referred to in any paragraph of subsection (a). . (C) Application to railroad retirement (i) In general Section 3231(e)(2)(A) of the Internal Revenue Code of 1986 is amended by adding at the end the following new clause: (iv) Limitation on exclusion For purposes of so much of the taxes imposed by sections 3201(a), 3211(a) and 3221(a) as are determined by reference to the rate in effect under section 3101(a) or 3111(a)— (I) in the case of any calendar year in which the contribution and benefit base (as determined under section 230 of the Social Security Act) is less than $400,000, clause (i) shall not apply to that part of the remuneration paid to an individual after remuneration of $400,000 for services rendered as an employee has been paid to such individual by an employer (or any person related to, or acting on behalf of, such employer, as determined by the Secretary) during the calendar year, and (II) in the case of any calendar year in which such contribution and benefit base equals or exceeds $400,000, clause (i) shall not apply. . (ii) Exclusion of remuneration which is not treated as compensation Section 3231(e)(2)(A)(ii) of the