Your argument next in case 23-129 M&K employee solutions versus the trustees of the IAM National Pension Fund.

Mr. Conelli.

Thank you, Mr. Chief Justice, and may it please the Court.

Section 1391 creates a clear timing rule.

Withdraw liability is based on the plan's unfunded vested benefits as of the end

of the prior year. The statute then defines unfunded vested benefits as the value of the plan's

non-forfeitable benefits minus the value of the plan's assets. That first number is the present

value of decades of future pension payments.

So the assumptions that the plan actuary makes about the future are a crucial part of what

determines that number. Changing the assumptions changes the present value and thus changes

the amount of unfunded vested benefits. But under the statute's timing rule, that amount is frozen on the valuation date.

Later changes in that amount cannot factor into the employer's liability.

That's just as true for changes caused by new assumptions as it is for changes from any other

component of the computation.

Respondents argue that until recently, actuaries have often selected withdrawal liability

assumptions after the valuation date. It's not clear that that's true, but even if it is,

it doesn't alter the meaning of the statutory text. And respondents themselves concede that plans and

actuaries can readily comply with our reading of the statute and in recent years have started to do so.

That makes sense our reading promotes predictability and consistency through a clear and simple rule.

Respondents' reading does the opposite. For them, actuarial assumptions can be

changed any time, including after the employer withdraws, even if the change triples or quadruples

what the employer believed it would owe. There's no reason to read the statute as creating

...