26 CFR § 31.3121(a)(5)-2 - Payments under or to an annuity contract described in section 403(b).
(a) Salary reduction agreement defined. For purposes of section 3121(a)(5)(D), the term salary reduction agreement means a plan or arrangement (whether evidenced by a written instrument or otherwise) whereby payment will be made by an employer, on behalf of an employee or his or her beneficiary, under or to an annuity contract described in section 403(b) -
(2) If the employee elects to reduce his or her compensation pursuant to a one-time irrevocable election made at or before the time of initial eligibility to participate in such plan or arrangement (or pursuant to a similar arrangement involving a one-time irrevocable election); or
(b) Effective/applicability date. This section is applicable on November 15, 2007.
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