Supreme Court Decides M & K Employee Solutions, LLC v. Trustees of the IAM National Pension Fund

On May 21, 2026, the US Supreme Court decided M & K Employee Solutions, LLC v. Trustees of the IAM National Pension Fund, 23-1209, holding that, under the Employee Retirement Income Security Act of 1974 (ERISA), an actuary for an underfunded multiemployer pension plan may calculate an employer's withdrawal liability based on actuarial assumptions adopted after the relevant measurement date for withdrawal liability. In other words, the actuary is not required to select actuarial assumptions “as of" the measurement date.

The case involved multiemployer pension plans, which are plans where more than one employer contributes to fulfill the terms of a collective bargaining agreement. When a multiemployer pension plan is underfunded, however, employers can only withdraw from the plan if they pay “withdrawal liability." 29 U.S.C. § 1381(a). Withdrawal liability is the employer's share of the plan's unfunded vested benefits “as of" the last day of the plan year preceding the employer's withdrawal — the measurement date. 29 U.S.C. § 1391. 

Unfunded vested benefits are not, however, a matter of simple math. They have to be estimated using certain hard data about the plan and its participants along with predictive actuarial judgments about the plan's future, including things like how long participants will obtain benefits. Then, the estimated future benefits have to be discounted to today's dollars using a certain discount rate. 

A month before the relevant measurement date (i.e., the last day of the plan year preceding the withdrawal), the plan's actuary used a certain discount rate to calculate unfunded vested benefits for an annual valuation. A month after the measurement date, the plan's actuary selected a lower discount rate to calculate unfunded vested benefits for withdrawal liability, which would become applicable to the employers. The difference in the discount rates resulted in greater withdrawal liability for the employers. 

The employers commenced arbitration actions against the plan sponsor to challenge the actuarial assumptions on which their withdrawal liability was based, arguing that the actuary was required to use assumptions selected “as of" the measurement date. The arbitrators agreed. District courts, and later the Court of Appeals for the D.C. Circuit, disagreed, reasoning that actuaries may use actuarial assumptions adopted after the measurement date to determine withdrawal liability. 

The Supreme Court affirmed. It first observed that withdrawal liability generally is addressed by 29 U.S.C. § 1391, which requires liability to be determined “as of" a particular date. Citing dictionaries, the Court determined that the phrase “as of" has a particular meaning: it requires a determination based on hard data from a particular date, but that determination can be made at a later point in time. Only the “hard data" needs to be fixed “as of" the measurement date, and that hard data does not include the actuarial assumptions used as a “tool" for a particular calculation or measurement. Because the actuarial assumption is not a factual input, the Court reasoned, it does not need to be selected “as of" measurement date. 

The Supreme Court then reviewed 29 U.S.C. § 1393, which “governs the use of actuarial assumptions for assessing withdrawal liability." Under this section, actuarial assumptions must be “reasonable," “take into account the experience of the plan and reasonable expectations," and must “offer the actuary's best estimate of anticipated experience under the plan." This section has no deadline; it requires reasonableness. Moreover, the Supreme Court looked to another ERISA section, § 1399, which addresses actuarial assumptions for other purposes and does specify a deadline. Because Congress included a deadline in that section, but not in § 1393, the Court presumed Congress's omission was intentional. 

Justice Jackson delivered the unanimous opinion of the Court.