When the Justice Department indicted the Southern Poverty Law Center in April on controversial fraud charges, the storied civil rights organization faced a major threat to its lifeblood — the flow of donor dollars.

Not because it was convicted or because the Internal Revenue Service revoked its tax-exempt status. Not even because individual donors stopped writing checks.

Instead, three Wall-Street-affiliated grantmaking giants each made a decision, one they refused to fully explain, to prevent donors from using their platforms to give to the embattled nonprofit.

Vanguard Charitable, Fidelity Charitable and Charles Schwab’s DAFgiving360 sponsor donor-advised funds, offering account holders immediate tax deductions on contributions they can later recommend be granted to charities.