On May 21, 2026, a unanimous Supreme Court issued a significant decision reshaping how withdrawal liability is calculated under the Employee Retirement Income Security Act (ERISA). In M & K Employee Solutions, LLC v. Trustees of IAM National Pension Fund, the Court held that plan actuaries may apply demographic and economic assumptions adopted after the statutory measurement date when assessing an employer's withdrawal liability from a multiemployer pension plan. The opinion, authored by Justice Ketanji Brown Jackson, resolves a question that has generated considerable disagreement among the lower courts and arbitration panels for years.
The decision turns on a careful balance between actuarial flexibility and statutory fidelity. While the Court endorsed the use of assumptions formally adopted after the measurement date, it conditioned that flexibility on an important safeguard: those assumptions must reflect only data and conditions that existed on or before the measurement date itself. In other words, actuaries may refine the analytical lens they apply, but the underlying facts must remain frozen as of the measurement date. This preserves the longstanding statutory snapshot principle that anchors ERISA's withdrawal liability framework.
For contributing employers, the practical implications are considerable. By expanding the actuarial latitude available to plan trustees, the ruling makes it more likely that withdrawal liability assessments will be calculated using assumptions designed to reflect persistent funding shortfalls, demographic trends, and broader economic realities. Employers contemplating an exit from an underfunded multiemployer pension plan should anticipate the prospect of materially higher liability determinations than may have been projected under prior practice.
In light of the decision, employers contributing to multiemployer plans should consider revisiting their withdrawal liability exposure modeling and stress-testing prior estimates against the broader range of assumptions trustees may now defensibly apply. Companies engaged in restructuring activity, mergers and acquisitions, or workforce realignments involving union-represented employees should pay particular attention, as funding-driven liabilities can meaningfully affect deal economics and ongoing operations. Coordination with actuarial advisors and ERISA counsel will be increasingly important when evaluating contingent liabilities and bargaining strategies.
This article provides a general overview and is not legal advice. Clients facing decisions regarding multiemployer pension plan participation or withdrawal should consult counsel for guidance tailored to their specific circumstances.