A voluntary plan in force and effect at the time a successor acquires the organization, trade, or business, or substantially all the assets thereof, or a distinct and severable portion of the organization, trade, or business, and continues its operation without substantial reduction of personnel resulting from the acquisition, must continue the voluntary plan and may not withdraw the plan without a specific request for withdrawal in a manner and at a time specified by the commissioner. A successor may terminate a voluntary plan with notice to the commissioner and without a request to withdraw the plan within ninety days from the date of the acquisition.