Former Labor Department executives and lawyers' groups joined the filing, arguing the rule hinders challenges to excessive fees and poor retirement-plan investments.
The case could reshape how defined-contribution plan participants sue over plan costs, by weakening a standard critics say screens out legitimate claims.
The dispute centres on retirement-plan litigation and could affect oversight of employer-sponsored savings plans if the court changes the benchmark test.
As 401(k) fee lawsuits surge, is the industry's pivot to passive investing and alternatives a genuine fix or a new risk?
Beyond fee lawsuits and passive funds, how will the system solve the core crisis: turning 401(k) savings into lifetime income?
With millions lacking retirement access, are new government IRAs the answer, or a distraction from 401(k) system flaws?