26 C.F.R. § 1.907(b)-1
If the foreign law imposing a FORI tax (as defined in § 1.907(c)-3 ) is either structured in a manner, or operates in a manner, so that the amount of tax imposed on FORI is generally materially greater than the tax imposed by the foreign law on income that is neither FORI nor FOGEI ("described manner"), section 907(b) provides a special rule which limits the amount of FORI taxes paid or accrued by a person to a foreign country which will be considered income, war profits, or excess profits taxes. Section 907(b) will apply to a person regardless of whether that person is a dual capacity taxpayer as defined in § 1.901-2(a)(2)(ii)(A) . (In general, a dual capacity taxpayer is a person who pays an amount to a foreign country part of which is attributable to an income tax and the remainder of which is a payment for a specific economic benefit derived from that country.) Foreign law imposing a tax on FORI will be considered either to be structured in or to operate in the described manner only if, under the facts and circumstances, there has been a shifting of tax by the foreign country from a tax on FOGEI to a tax on FORI.
26 C.F.R. §1.907(b)-1