(a) Application of section. Section 401(a)(19) and this section apply to a plan to which section 411(a) applies. (See section 411(e) and § 11.411(a)-2 for applicability of section 411.)

(b) Prohibited forfeitures—(1) General rule. A plan to which this section applies is not a qualified plan (and a trust forming a part of such plan is not a qualified trust) if, under such plan, any part of a participant's accrued benefit derived from employer contributions is forfeitable solely because a benefit derived from the participant's contributions under the plan is voluntarily withdrawn by him after he has become a 50 percent vested participant.

(2) 50 percent vested participant. For purposes of paragraph (b)(1) of this section, a participant is a 50 percent vested participant when he has a nonforfeitable right (within the meaning of section 411 and the regulations thereunder) to at least 50 percent of his accrued benefit derived from employer contributions.

(3) Certain forfeitures. Paragraph (b)(1) of this section does not apply in the case of a forfeiture permitted by section 411(a)(3)(D)(iii) and § 11.411(a)-4(b)(5)(i) (relating to forfeitures of certain benefits accrued before September 2, 1974).