29 C.F.R. § 4043.63

(a) Reportable event and information required. Advance notice is required for a liquidation of a member of a plan's controlled group, as described in § 4043.30(a), and the notice shall include the information described in § 4043.30(b) and, if known, the expected effective date of the reportable event.

(b) Waiver. Notice is waived if the person that liquidates is a de minimis 5-percent segment of the plan's controlled group for the most recent fiscal year(s) ending on or before the effective date of the reportable event, and each plan that was maintained by the liquidating member is maintained by another member of the plan's controlled group.