29 C.F.R. § 4207.9 – Special rules.

(a) Employer that has withdrawn and reentered the plan before the effective date of this part. This part shall apply, in accordance with the rules in this paragraph, with respect to an eligible employer that completely withdraws from a multiemployer plan after September 25, 1980, and is performing covered work under the plan on the effective date of this part. Upon the application of an employer described in the preceding sentence, the plan sponsor of a multiemployer plan shall determine whether the employer satisfies the requirements for abatement of its complete withdrawal liability under this part. Pending the plan sponsor's determination, the employer may provide the plan with a bond or escrow that satisfies the requirements of § 4207.4, in lieu of making its withdrawal liability payments due after its application for an abatement determination. The plan sponsor shall notify the employer in writing of its determination and the consequences of its determination as described in § 4207.3 (c) or (d) and (e), as applicable. If the plan sponsor determines that the employer qualifies for abatement, only withdrawal liability payments made prior to the employer's reentry shall be retained by the plan; payments made by the employer after its reentry shall be refunded to the employer, with interest on those made prior to the application for abatement, in accordance with § 4207.3(e)(2). If a bond or escrow has been provided to the plan in accordance with § 4207.4, the plan sponsor shall send a copy of the notice to the bonding or escrow agent. Sections 4207.6 through 4207.8 shall apply with respect to the employer's subsequent complete withdrawal occurring on or after the effective date of this part, or partial withdrawal occurring either before or after that date. This paragraph shall not negate reasonable actions taken by plans prior to the effective date of this part under plan rules implementing section 4207(a) of ERISA that were validly adopted pursuant to section 405 of the Multiemployer Act.
(b) Employer with multiple complete withdrawals that has reentered the plan before effective date of this part. If an employer described in paragraph (a) of this section has completely withdrawn from a multiemployer plan on two or more occasions before the effective date of this part, the rules in paragraph (a) of this section shall be applied as modified by this paragraph.
1. (1) The plan sponsor shall determine whether the employer satisfies the requirements for abatement under § 4207.5 based on the most recent complete withdrawal.
2. (2) If the employer satisfies the requirements for abatement, the employer's liability with respect to all previous complete withdrawals shall be abated.
3. (3) If the liability is abated, §§ 4207.6 and 4207.7 shall be applied as if the employer's earliest complete withdrawal were its initial complete withdrawal.
(c) Employer with multiple complete withdrawals that has not reentered the plan as of the effective date of this part. If an eligible employer has completely withdrawn from a multiemployer plan on two or more occasions between September 26, 1980, and the effective date of this part and is not performing covered work under the plan on the effective date of this regulation, the rules in this part shall apply, subject to the modifications specified in paragraphs (b)(1)-(b)(3) of this section, upon the employer's reentry into the plan.
(d) Combination of withdrawn employer with contributing employer. If a withdrawn employer merges or otherwise combines with an employer that has an obligation to contribute to the plan from which the first employer withdrew, the combined entity is the eligible employer, and the rules of § 4207.5 shall be applied—
1. (1) By subtracting from the measurement period contribution base units the contribution base units for which the non-withdrawn portion of the employer was obligated to contribute in the last plan year ending prior to the combination;
2. (2) By determining the base year contribution base units solely by reference to the contribution base units of the withdrawn portion of the employer; and
3. (3) By using the date of the combination, rather than the date of resumption of covered operations, to begin the measurement period.
(e) Combination of two or more withdrawn employers. If two or more withdrawn employers merge or otherwise combine, the combined entity is the eligible employer, and the rules of § 4207.5 shall be applied by combining the number of contribution base units with respect to which each portion of the employer had an obligation to contribute under the plan for its base year. However, the combined number of contribution base units shall not include contribution base units of a withdrawn portion of the employer that had fully paid its withdrawal liability as of the date of the resumption of covered operations.