Vanguard Group Inc. is walking out of the world's largest climate-finance alliance, marking the coalition's biggest defection to date as Republicans step up their threats against firms deemed hostile toward the fossil-fuel industry.

Vanguard's decision followed a "considerable period of review," according to a company statement Wednesday. Last week, 13 Republican state attorneys general asked federal energy officials to consider blocking Vanguard from buying utility stocks because of its relationships with anti-coal and anti-natural gas activists.

Withdrawing from the Net Zero Asset Managers initiative, which is a sub-unit of the Glasgow Financial Alliance for Net Zero, "will help provide the clarity our investors desire" about everything from the role of index funds, to financial risks in the context of climate change, the firm said.