Overpayment by Multiemployer Plan

[Miner88]

When an overpayment is made from a plan, the EPCRS rev. proc. says that the employer must make reasonable efforts to collect the overpayment and, to the extent it cannot be recovered, then the employer or another person must contribute the difference to the plan. In the defined benefit multiemployer context, who makes the payment to make the plan whole? Any thoughts would be appreciated!