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.

Malvern-based Vanguard is pricing active funds cheaper as it competes with Schwab, Fidelity, and other mass-market money managers.

Vanguard is already a dominant player in equity investing, thanks to its enormous index-tracking funds and relatively low-cost active funds. It runs the world’s largest investment fund, a $1.78tn behemoth that tracks the entire US market, and its S&P 500 ETF is the world’s second-largest and closing in on the market leader.

The world’s second-largest asset manager has slashed the cost of fund investing, in a record move that is expected to save investors more than $350 million this year alone.

Vanguard made headlines by touting what it called “our largest-ever reduction in expense ratios.” The asset manager known for rock-bottom costs, said it was reducin