(a) Except as otherwise provided in this section, this part shall apply in the case of plan years beginning after September 2, 1974.

(b)

(1) Except as otherwise provided in subsection (d), sections 1055, 1056(d) and 1058 of this title shall apply with respect to plan years beginning after December 31, 1975.

(2) Except as otherwise provided in subsections (c) and (d) in the case of a plan in existence on January 1, 1974, this part shall apply in the case of plan years beginning after December 31, 1975.

(c)

(1) In the case of a plan maintained on January 1, 1974, pursuant to one or more agreements which the Secretary finds to be collective bargaining agreements between employee organizations and one or more employers, no plan shall be treated as not meeting the requirements of sections 1054 and 1055 of this title by reason of a supplementary or special plan provision (within the meaning of paragraph (2)) for any plan year before the year which begins after the earlier of—

(A) the date on which the last of such agreements relating to the plan terminates (determined without regard to any extension thereof agreed to after September 2, 1974), or

(B) December 31, 1980.

For purposes of subparagraph (A) and section 1086(c) ¹ of this title, any plan amendment made pursuant to a collective bargaining agreement relating to the plan which amends the plan solely to conform to any requirement contained in this chapter or title 26 shall not be treated as a termination of such collective bargaining agreement. This paragraph shall not apply unless the Secretary determines that the participation and vesting rules in effect on September 2, 1974, are not less favorable to participants, in the aggregate, than the rules provided under sections 1052, 1053, and 1054 of this title.

(2) For purposes of paragraph (1), the term "supplementary or special plan provision" means any plan provision which—

(A) provides supplementary benefits, not in excess of one-third of the basic benefit, in the form of an annuity for the life of the participant, or

(B) provides that, under a contractual agreement based on medical evidence as to the effects of working in an adverse environment for an extended period of time, a participant having 25 years of service is to be treated as having 30 years of service.

(3) This subsection shall apply with respect to a plan if (and only if) the application of this subsection results in a later effective date for this part than the effective date required by subsection (b).

(d) If the administrator of a plan elects under section 1017(d) of this Act to make applicable to a plan year and to all subsequent plan years the provisions of title 26 relating to participation, vesting, funding, and form of benefit, this part shall apply to the first plan year to which such election applies and to all subsequent plan years.

(e)

(1) No pension plan to which section 1052 of this title applies may make effective any plan amendment with respect to breaks in service (which amendment is made or becomes effective after January 1, 1974, and before the date on which section 1052 of this title first becomes effective with respect to such plan) which provides that any employee's participation in the plan would commence at any date later than the later of—

(A) the date on which his participation would commence under the break in service rules of section 1052(b) of this title, or

(B) the date on which his participation would commence under the plan as in effect on January 1, 1974.

(2) No pension plan to which section 1053 of this title applies may make effective any plan amendment with respect to breaks in service (which amendment is made or becomes effective after January 1, 1974, and before the date on which section 1053 of this title first becomes effective with respect to such plan) if such amendment provides that the nonforfeitable benefit derived from employer contributions to which any employee would be entitled is less than the lesser of the nonforfeitable benefit derived from employer contributions to which he would be entitled under—

(A) the break in service rules of section 1052(b)(3) of this title, or

(B) the plan as in effect on January 1, 1974.

Subparagraph (B) shall not apply if the break in service rules under the plan would have been in violation of any law or rule of law in effect on January 1, 1974.

(f) The preceding provisions of this section shall not apply with respect to amendments made to this part in provisions enacted after September 2, 1974.