Who sets the rules for exiting pension plans?

Overview

Updated May 22

When employers exit multiemployer pension plans, they owe a share of unfunded benefits—a calculation that hinges on assumptions about future investment returns. The IAM National Pension Fund changed its interest rate assumption from 7.5% to 6.5% in January 2018, weeks after the measurement date, and applied it retroactively to employers who had already withdrawn. The result: withdrawal liabilities tripled from $935 million to over $3 billion.

The Supreme Court heard oral arguments on January 20, 2026, and justices appeared skeptical of employers' attempts to impose strict timing restrictions on actuarial assumptions. Justice Brett Kavanaugh emphasized that ERISA requires actuaries to use 'reasonable methods' to make their 'best estimate' of pension fund performance, characterizing employer arguments as facing high 'hurdles.' The Court appeared poised to side with pension fund actuaries, potentially allowing them to use the most current data available when calculating withdrawal liability.

A decision is expected by late June 2026.

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Key Indicators

1,400

Multiemployer plans affected

Number of pension plans nationwide that will be bound by the ruling

11M

Covered workers

Participants in multiemployer pension plans impacted by the decision

600%

Liability increase

How much M&K's withdrawal liability grew after the retroactive rate change

Interest rate change

The drop from 7.5% to 6.5% that triggered the dispute

Voices

Curated perspectives — historical figures and your fellow readers.

Ever wondered what historical figures would say about today's headlines?

People Involved

Michael E. Kenneally

Lead Counsel for Petitioners

Argued before Supreme Court on January 20, 2026

John G. Roberts Jr.

Lead Counsel for Respondent

Representing IAM National Pension Fund trustees

Organizations Involved

IAM National Pension Fund

Multiemployer Pension Plan

Respondent in Supreme Court case

Multiemployer pension plan covering employees represented by the International Association of Machinists and Aerospace Workers union.

M&K Employee Solutions, LLC

Private Employer

Lead petitioner in Supreme Court case

Former contributing employer to the IAM National Pension Fund that withdrew in 2018.

U.S. Chamber of Commerce

Business Advocacy Organization

Filed amicus brief supporting employers

Largest business lobbying organization in the United States, representing more than 3 million businesses.

Pension Benefit Guaranty Corporation

Federal Agency

Supported certiorari; filed brief through Solicitor General

Federal agency that insures private-sector pension benefits and oversees multiemployer plan solvency.

National Coordinating Committee for Multiemployer Plans

Industry Advocacy Organization

Filed amicus brief supporting pension fund

Coalition of employer associations, labor unions, and professionals advocating for multiemployer pension plan interests.

Timeline

September 1980 January 2026

14 events Latest: January 20th, 2026 · 8 months ago Showing 8 of 14

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January 2026
Supreme Court Hears Oral Arguments
Latest Legal

Justices hear arguments on whether pension plans can retroactively apply actuarial assumptions when calculating withdrawal liability.
January 20th, 2026
Justices Signal Skepticism Toward Employer Position
Legal

During oral arguments, multiple justices questioned employers' push to restrict actuaries from updating assumptions after year-end. Justice Kavanaugh emphasized ERISA's requirement that actuaries use 'reasonable methods' for their 'best estimate,' suggesting employer arguments face 'hurdles.'
January 20th, 2026
June 2025
Supreme Court Grants Certiorari
Legal

The Court agrees to hear M&K Employee Solutions v. Trustees of the IAM National Pension Fund.
June 30th, 2025
May 2025
Solicitor General Supports Certiorari
Legal

The Solicitor General, with PBGC support, files a brief urging the Court to resolve the 'clear conflict' affecting 1,400 multiemployer plans.
May 27th, 2025
October 2024
Court Invites Solicitor General's Views
Legal

The Supreme Court requests the U.S. government's position on whether to hear the case.
October 7th, 2024
May 2024
M&K Petitions Supreme Court
Legal

M&K Employee Solutions files a petition for certiorari, asking the Supreme Court to resolve the circuit split.
May 9th, 2024
February 2024
D.C. Circuit Rules for Pension Fund
Legal

The D.C. Circuit holds that actuaries may adopt assumptions after the measurement date if based on information available 'as of' that date, creating a circuit split.
February 9th, 2024
January 2020
Second Circuit Rules for Employers in Metz
Legal

In National Retirement Fund v. Metz Culinary Management, the Second Circuit holds actuarial assumptions must be locked in as of the measurement date.
January 2nd, 2020
January 2018
Fund Adopts 6.5% Rate Retroactively
Administrative

After a board meeting, the IAM fund's actuary adopts a 6.5% interest rate and applies it to calculate withdrawal liability for employers who left in 2018.
January 2018
2018
M&K and Ohio Magnetics Withdraw from Fund
Event

Multiple employers including M&K Employee Solutions and Ohio Magnetics withdraw from the IAM National Pension Fund during 2018.
2018
December 2017
Measurement Date for 2018 Withdrawals
Administrative

The statutory date 'as of' which withdrawal liability must be calculated for employers leaving the IAM fund in 2018.
December 31st, 2017
November 2017
IAM Fund Uses 7.5% Interest Rate
Administrative

The IAM National Pension Fund's actuary sets the interest rate assumption at 7.5% for funding valuations.
November 2017
June 1993
Supreme Court Upholds MPPAA in Concrete Pipe
Legal

In Concrete Pipe v. Construction Laborers Pension Trust, the Court rules withdrawal liability is constitutional, establishing that it creates a 'fixed and certain debt.'
June 14th, 1993
September 1980
MPPAA Establishes Withdrawal Liability Framework
Legislation

President Carter signs the Multiemployer Pension Plan Amendments Act, requiring employers leaving underfunded pension plans to pay their share of unfunded benefits.
September 26th, 1980

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Scenarios

Employers Win: Assumptions Locked at Year-End

Possible

Discussed by: U.S. Chamber of Commerce, employer-side ERISA practitioners, business publications

The Court rules that withdrawal liability must be calculated using actuarial assumptions in effect at the measurement date. This would give employers predictable exit costs, potentially encouraging more businesses to join multiemployer plans. However, pension funds would lose flexibility to use the most current data, which actuaries argue produces more accurate liability assessments. The IAM fund and similar plans would need to recalculate billions in withdrawal liability for employers who withdrew after rate changes.

Pension Fund Wins: 'As Of' Interpretation Prevails

Possible

Discussed by: NCCMP, PBGC, labor-side attorneys, pension fund administrators

The Court affirms the D.C. Circuit, holding that actuaries may adopt assumptions after the measurement date as long as they reflect conditions 'as of' that date. This preserves fund flexibility to incorporate the latest available information, which proponents argue better protects plan solvency and participant benefits. Employers would face less certainty about withdrawal costs, but the Solicitor General argued this interpretation aligns with ERISA's purpose of protecting participants.

Narrow Ruling on Timing, Broader Questions Deferred

Possible

Discussed by: ERISA scholars, Supreme Court analysts

The Court issues a narrow ruling focused on statutory interpretation of 'as of the end of the plan year' without establishing bright-line rules for all actuarial assumption changes. This would resolve the immediate circuit split but leave questions about the scope of permissible assumption changes for future litigation. Pension plans and employers would continue operating under some uncertainty pending further regulatory or legislative clarification.

Congress Intervenes with Statutory Fix

Unlikely

Discussed by: Legislative observers, NCCMP policy advocates

Regardless of the Court's ruling, Congress acts to clarify ERISA's withdrawal liability provisions. This could occur if the decision creates significant disruption for either employers or pension funds. The Multiemployer Pension Reform Act of 2014 and American Rescue Plan of 2021 showed Congress's willingness to intervene in multiemployer pension issues when systemic stability is at stake.

Historical Context

3 moments from history that rhyme with this story — and how they unfolded.

September 1980

MPPAA Passage (1980)

Congress passed the Multiemployer Pension Plan Amendments Act to address a wave of employer withdrawals that were destabilizing pension plans. Before MPPAA, employers could exit plans without paying their share of unfunded benefits, leaving remaining employers and the PBGC holding the bag.

Then

MPPAA imposed withdrawal liability on departing employers, requiring them to pay their allocable share of unfunded vested benefits.

Now

The law stabilized the multiemployer system for decades but created an exit barrier that some argue traps employers in troubled plans. Courts have since grappled with how to calculate liability fairly.

Why this matters now

The current dispute centers on MPPAA's requirement to calculate liability 'as of the end of the plan year.' Congress's 1980 intent—balancing employer predictability against plan solvency—is at the heart of the interpretive question before the Court.

June 1993

Concrete Pipe & Products v. Construction Laborers Pension Trust (1993)

An employer challenged the constitutionality of MPPAA withdrawal liability after being assessed a share of unfunded benefits upon leaving a multiemployer pension plan. The employer argued the assessment violated due process and constituted an unconstitutional taking of property.

Then

The Supreme Court upheld MPPAA, ruling that withdrawal liability was constitutional and describing it as a 'fixed and certain debt' that employers assumed by participating in the plan.

Now

The decision established the legal foundation for withdrawal liability, confirming Congress's authority to impose financial obligations on departing employers. It remains the leading precedent in ERISA multiemployer cases.

Why this matters now

The current case tests what 'fixed and certain' means in practice. If assumptions can change after the measurement date, employers argue the debt is neither fixed nor certain when they make withdrawal decisions.

December 2022

Central States Teamsters Pension Fund Bailout (2022)

The Central States, Southeast & Southwest Areas Pension Fund received $35.8 billion from the PBGC's Special Financial Assistance program—the largest single pension bailout in U.S. history. The fund, which covered 357,000 Teamsters, had been projected to run out of money by 2025 due to decades of underfunding and employer withdrawals.

Then

The bailout restored the fund's ability to pay full benefits through 2051, avoiding cuts of up to 40% for retirees.

Now

The program demonstrated federal willingness to backstop troubled multiemployer plans but raised questions about moral hazard and whether remaining employers should bear exit costs when federal assistance is available.

Why this matters now

The Central States crisis shows what happens when employer withdrawals accelerate: remaining employers face growing liability, more exit, and the fund spirals toward insolvency. Today's case affects incentives for employers considering withdrawal.