Vanguard Group Inc.’s biggest salvo yet in its campaign to cut fees for the investing masses presents industry rivals with a painful choice. Follow suit and lose potentially hundreds of millions in revenue — or hold the line and risk losing badly needed market share.

Vanguard Group Inc., the world's second-largest ETF issuer, is making what it says is its biggest fee cuts in the company's 50-year history, trimming the expense ratios of dozens of mutual fund and ETF share classes that it claims will save investors more than $350 million in 2025.

Even if they don’t cut fees, active managers need to determine whether prices are still fair and that their funds offer something that can’t be replaced with passive.