A price war is intensifying in the $3.5tn exchange traded fund industry, forcing some of the biggest firms to slash fees in a bare-knuckled bid to win a larger slice of the fast-growing market.

BlackRock cut fees on several stock and bond ETFs last month, while State Street introduced last fall a new low-cost lineup of more than a dozen funds. The latest volley came last week when Vanguard eliminated online transaction fees for virtually all ETFs bought and sold through its brokerage platform, including rivals’ funds.