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.

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

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.

Vanguard Group (VOO), one of the world's largest ETF issuers, announced it is reducing fees on 168 mutual funds and ETF-related share classes, potentially saving investors over $350 million this year.

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.

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.

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