On May 21, 2026, the US Supreme Court issued a unanimous decision in M & K Employee Solutions, LLC v. Trustees of the IAM National Pension Fund, No. 23-1209, resolving a circuit split on a question of enormous financial consequence to employers participating in multiemployer pension plans (MPPs): whether a plan’s actuary must adopt its actuarial assumptions for purposes of withdrawal liability calculations on or before the “measurement date” for those calculations, or whether it may instead select assumptions after that date. In an opinion authored by Justice Jackson, the Court held that ERISA does not require actuarial assumptions to be adopted “as of” the measurement date, but stressed that these actuarial assumptions must still reflect the actuary’s “best estimate of anticipated experience under the plan,” which generally requires that the assumptions reflect information about the plan’s conditions as they stood on the measurement date.
Background
Under ERISA and the Multiemployer Pension Plan Amendments Act of 1980 (MPPAA), an employer that withdraws from an underfunded MPP must pay “withdrawal liability,” which is its proportionate share of the plan’s unfunded vested benefits (UVBs). The statute requires this liability to be calculated “as of” the last day of the plan year preceding the employer’s withdrawal, or the “measurement date.” Calculating UVBs requires actuarial assumptions about the plan and its future benefit obligations, most notably a discount rate that converts the plan’s future liabilities to present-day dollars. The discount rate dramatically affects the total withdrawal liability figure.