According to PBGC, 61 plans filed notices for 2020 that they were in Critical and Declining status.
There have been 32 plans that filed for benefit cuts under MPRA and it may pay off for every other multiemployer plan to rustle up a submission package prior to enactment.
Then we come to other plans who might be (or could make themselves) eligible. Of 1,220 plans who filed Schedule MBs for 2018 there were:
118 in Critical and Declining status
638 with more retired than active participants
1202 with unfunded liabilities
$685 billion in net unfunded liabilities
Author(s): John Bury
Publication Date: 9 March 2021
Publication Site: Burypensions