Late actuarial tweaks just turned a $1.8M bill into $6.2M – and the high court is fine with it

Employers just lost a unanimous Supreme Court fight over pension exit bills, and the math can swing by millions.

A unanimous US Supreme Court ruled on May 21, 2026 that multiemployer pension plans can use actuarial assumptions adopted after the official measurement date to calculate what a withdrawing employer owes. The decision was written by Justice Jackson. It is a clean win for plans and a hard loss for employers trying to exit them.

For HR and benefits leaders at companies that participate in union pension plans, the message is blunt. Withdrawal liability, the share of a plan's unfunded benefits an employer must cover on the way out, can grow significantly between the date a company decides to leave and the date the bill lands. The court has now confirmed that federal law allows it.

The case involved four employers who withdrew from the IAM National Pension Fund, an underfunded plan covering workers represented by the International Association of Machinists and Aerospace Workers, between April and December 2018.

In November 2017, the Fund's actuary, Cheiron, valued the plan's unfunded vested benefits at close to $500 million using a 7.50% discount rate. Two months later, in January 2018, the Fund and Cheiron settled on a lower rate of 6.50%. A lower discount rate makes future benefit obligations look bigger in today's dollars. When Cheiron published the 2017 plan year...

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