26 C.F.R. § 1.269-4
The district director is authorized by section 269(b) to allow a part of the amount disallowed by section 269(a), but he may allow such part only if and to the extent that he determines that the amount allowed will not result in the evasion or avoidance of Federal income tax for which the acquisition was made. The district director is also authorized to use other methods to give effect to part of the amount disallowed under section 269(a), but only to such extent as he determines will not result in the evasion or avoidance of Federal income tax for which the acquisition was made. Whenever appropriate to give proper effect to the deduction, credit, or other allowance, or such part of it which may be allowed, this authority includes the distribution, apportionment, or allocation of both the gross income and the deductions, credits, or other allowances the benefit of which was sought, between or among the corporations, or properties, or parts thereof, involved, and includes the disallowance of any such deduction, credit, or other allowance to any of the taxpayers involved.
26 C.F.R. §1.269-4