26 U.S.C. § 269A: Personal service corporations formed or availed of to avoid or evade income tax

substantially all of the services of a personal service corporation are performed for (or on behalf of) 1 other corporation, partnership, or other entity, and the principal purpose for forming, or availing of, such personal service corporation is the avoidance or evasion of Federal income tax by reducing the income of, or securing the benefit of any expense, deduction, credit, exclusion, or other allowance for, any employee-owner which would not otherwise be available, The term “personal service corporation” means a corporation the principal activity of which is the performance of personal services and such services are substantially performed by employee-owners. The term “employee-owner” means any employee who owns, on any day during the taxable year, more than 10 percent of the outstanding stock of the personal service corporation. For purposes of the preceding sentence, section 318 shall apply, except that “5 percent” shall be substituted for “50 percent” in section 318(a)(2)(C). All related persons (within the meaning of section 144(a)(3)) shall be treated as 1 entity.