26 U.S.C. § 280C: Certain expenses for which credits are allowable

No deduction shall be allowed for that portion of the wages or salaries paid or incurred for the taxable year which is equal to the sum of the credits determined for the taxable year under sections 45A(a), 45P(a), 45S(a)(1)(A), 51(a), and 1396(a). No deduction shall be allowed for that portion of the premiums paid or incurred for the taxable year which is equal to that portion of the paid family and medical leave credit which is determined for the taxable year under section 45S(a)(1)(B). In the case of a corporation which is a member of a controlled group of corporations (within the meaning of section 52(a)) or a trade or business which is treated as being under common control with other trades or businesses (within the meaning of section 52(b)), this subsection shall be applied under rules prescribed by the Secretary similar to the rules applicable under subsections (a) and (b) of section 52. No deduction shall be allowed for that portion of the qualified clinical testing expenses (as defined in section 45C(b)) otherwise allowable as a deduction for the taxable year which is equal to the amount of the credit allowable for the taxable year under section 45C (determined without regard to section 38(c)). the amount of the credit allowable for the taxable year under section 45C (determined without regard to section 38(c)), exceeds the amount allowable as a deduction for the taxable year for qualified clinical testing expenses (determined without regard to paragraph (1)), paragraphs (1) and (2) shall not apply, and the amount of the credit under section 45C(a) shall be the amount determined under subparagraph (B). the amount of credit determined under section 45C(a) without regard to this paragraph, over the amount described in clause (i), and the maximum rate of tax under section 11(b). An election under this paragraph for any taxable year shall be made not later than the time for filing the return of tax for such year (including extensions), shall be made on such return, and shall be made in such manner as the Secretary shall prescribe. Such an election, once made, shall be irrevocable. In the case of a corporation which is a member of a controlled group of corporations (within the meaning of section 41(f)(5)) or a trade or business which is treated as being under common control with other trades or business (within the meaning of section 41(f)(1)(B)), this subsection shall be applied under rules prescribed by the Secretary similar to the rules applicable under subparagraphs (A) and (B) of section 41(f)(1). The domestic research or experimental expenditures (as defined in section 174A(b)) otherwise taken into account as a deduction or charged to capital account under this chapter shall be reduced by the amount of the credit allowed under section 41(a). paragraph (1) shall not apply, and the amount of the credit under section 41(a) shall be the amount determined under subparagraph (B). the amount of credit determined under section 41(a) without regard to this paragraph, over the amount described in clause (i), and the maximum rate of tax under section 11(b). An election under this paragraph for any taxable year shall be made not later than the time for filing the return of tax for such year (including extensions), shall be made on such return, and shall be made in such manner as the Secretary may prescribe. Such an election, once made, shall be irrevocable. Paragraph (3) of subsection (b) shall apply for purposes of this subsection. The deductions otherwise allowed under this chapter for the taxable year shall be reduced by the amount of the credit determined for the taxable year under section 45H(a). No deduction shall be allowed for that portion of the expenses otherwise allowable as a deduction for the taxable year which is equal to the amount of the credit determined for the taxable year under section 45N(a). No deduction shall be allowed for that portion of the expenses otherwise allowable as a deduction taken into account in determining the credit under section 45O for the taxable year which is equal to the amount of the credit determined for such taxable year under section 45O(a). No deduction shall be allowed for the portion of the premiums paid by the taxpayer for coverage of 1 or more individuals under a qualified health plan which is equal to the amount of the credit determined for the taxable year under section 36B(a) with respect to such premiums. No deduction shall be allowed for that portion of the premiums for qualified health plans (as defined in section 1301(a) of the Patient Protection and Affordable Care Act), or for health insurance coverage in the case of taxable years beginning in 2010, 2011, 2012, or 2013, paid by an employer which is equal to the amount of the credit determined under section 45R(a) with respect to the premiums. Except as otherwise provided in this subsection, the amendments made by this section [amending this section and sections 50A and 50B of this title] shall apply to work incentive program expenses paid or incurred after December 31, 1978 , in taxable years ending after such date; except that so much of the amendment made by subsection (a) as affects section 50A(a)(2) of the Internal Revenue Code of 1986 [formerly I.R.C. 1954] shall apply to taxable years beginning after December 31, 1978 . For purposes of applying section 50A(a)(2) of the Internal Revenue Code of 1986 with respect to a taxable year beginning before January 1, 1979 , the rules of sections 50A(a)(4), 50A(a)(5), and 50B(e)(3) of such Code (as in effect on the day before the date of the enactment of this Act [ Nov. 6, 1978 ] shall apply. In the case of any eligible employee (as defined in section 50B(h)) hired before September 27, 1978 , no credit shall be allowed under section 40 with respect to second-year work incentive program expenses (as defined in section 50B(a)) attributable to service performed by such employee. In the case of any eligible employee (as defined in section 50B(h)) hired after September 26, 1978 , for purposes of applying the amendments made by this section, such individual shall be treated for purposes of the credit allowed by section 40 as having first begun work for the taxpayer not earlier than January 1, 1979 , and any wages paid or incurred after December 31, 1978 , with respect to such individual shall be considered to be attributable to services rendered after that date.” at any time before the date which is 75 days after such date of enactment, and in such form and manner as the Secretary of the Treasury or his delegate may prescribe.”