For purposes of clause (i), a contribution shall be treated as not made pursuant to a salary reduction agreement if under the agreement it is made pursuant to a 1-time irrevocable election made by the employee at the time of initial eligibility to participate in the agreement or is made pursuant to a similar arrangement involving a one-time irrevocable election specified in regulations. For purposes of clause (ii), there may be excluded any employee who is a participant in an eligible deferred compensation plan (within the meaning of
section 457) or a qualified cash or deferred arrangement of the organization or another annuity contract described in this subsection. Any nonresident alien described in
section 410(b)(3)(C) may also be excluded. Subject to the conditions applicable under
section 410(b)(4), there may be excluded for purposes of this subparagraph employees who are students performing services described in
section 3121(b)(10) and employees who normally work less than 20 hours per week.