Interest paid to an employee by an employer under a nonqualified deferred compensation plan is not considered net investment income.

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Do you have a deferred compensation plan?

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As part of his employee contract with the Irish company, most of his salary is diverted into a nonqualified deferred-compensation plan, and held in a so-called Rabbi trust in a Caribbean tax haven, where it grows tax free.

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What's more, workers can invest in collective trusts only in ERISA-qualified plans, according to Ms. Nordquist. (ERISA stands for Employee Retirement Income Security Act.) That means CITs aren't available to retail individual retirement accounts, 403(b)s, government-sponsored 457(f) plans or any executive deferred-compensation non-qualified plan.

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