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.

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.

Investors have upped their interest in actively managed bond ETFs, pouring record capital into them in January as some paid up in hopes of stronger returns.

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.