Federal wages
(2) (A) With respect to Federal wages of an employee or Member (or that portion thereof) not exceeding the contribution and benefit base during the calendar year involved, the appropriate amount to be deducted and withheld under this subsection is the amount by which— (i) the total deduction for those wages (or for that portion) exceeds; (ii) the OASDI contribution with respect to those wages (or that portion). (B) With respect to any portion of Federal wages of an employee or Member which exceed the contribution and benefit base during the calendar year involved, the appropriate amount to be deducted and withheld under this subsection is an amount equal to the total deduction for that portion. (C) For purposes of this paragraph— (i) the term “Federal wages” means basic pay for service as an employee or Member, as the case may be; (ii) the term “contribution and benefit base” means the contribution and benefit base in effect with respect to the period involved, as determined under section 230 of the Social Security Act; (iii) the term “total deduction”, as used with respect to any Federal wages (or portion thereof), means an amount equal to the amount of those wages (or of that portion), multiplied by the percentage which (but for this subsection) would apply under subsection (a)(1)(A) with respect to the individual involved; and (iv) the term “OASDI contribution”, with respect to any income, means the amount of tax which may be imposed under section 3101(a) of the Internal Revenue Code of 1986 with respect to such income (determined without regard to any income which is not a part of Federal wages).