Treas. Reg. § 1.402(g)(3)-1

(a) General rule. With respect to an annuity contract under section 403(b), except as provided in paragraph (b) of this section, an elective deferral means an employer contribution to purchase an annuity contract under section 403(b) under a salary reduction agreement within the meaning of section 3121(a)(5)(D).

(b) Special rule. Notwithstanding paragraph (a) of this section, for purposes of section 403(b), an elective deferral only includes a contribution that is made pursuant to a cash or deferred election (as defined at § 1.401(k)-1(a)(3)). Thus, for purposes of section 402(g)(3)(C), an elective deferral does not include a contribution that is made pursuant to an employee's one-time irrevocable election made on or before the employee's first becoming eligible to participate under the employer's plans or a contribution made as a condition of employment that reduces the employee's compensation.

(c) Applicable date. This section is applicable for taxable years beginning after December 31, 2008.