29 USC 1411 - Mergers and transfers between multiemployer plans

(a) Authority of plan sponsor 
Unless otherwise provided in regulations prescribed by the corporation, a plan sponsor may not cause a multiemployer plan to merge with one or more multiemployer plans, or engage in a transfer of assets and liabilities to or from another multiemployer plan, unless such merger or transfer satisfies the requirements of subsection (b) of this section.
(b) Criteria 
A merger or transfer satisfies the requirements of this section if
(1) in accordance with regulations of the corporation, the plan sponsor of a multiemployer plan notifies the corporation of a merger with or transfer of plan assets or liabilities to another multiemployer plan at least 120 days before the effective date of the merger or transfer;
(2) no participants or beneficiarys accrued benefit will be lower immediately after the effective date of the merger or transfer than the benefit immediately before that date;
(3) the benefits of participants and beneficiaries are not reasonably expected to be subject to suspension under section 1426 of this title; and
(4) an actuarial valuation of the assets and liabilities of each of the affected plans has been performed during the plan year preceding the effective date of the merger or transfer, based upon the most recent data available as of the day before the start of that plan year, or other valuation of such assets and liabilities performed under such standards and procedures as the corporation may prescribe by regulation.
(c) Actions not deemed violation of section 1106 (a) or (b)(2) of this title 
The merger of multiemployer plans or the transfer of assets or liabilities between multiemployer plans, shall be deemed not to constitute a violation of the provisions of section 1106 (a) of this title or section 1106 (b)(2) of this title if the corporation determines that the merger or transfer otherwise satisfies the requirements of this section.
(d) Nature of plan to which liabilities are transferred 
A plan to which liabilities are transferred under this section is a successor plan for purposes of section 1322a (b)(2)(B) of this title.