Per this:

A longtime anonymous donor to the American Civil Liberties Union has withdrawn his annual gift of more than $20 million, punching a 25 percent hole in its annual operating budget and forcing cutbacks in operations... [Per the NYT, board members say that the donor is hedge fund manager and investor David Gelbaum]... (ACLU executive director Anthony Romero) said that donors like the Leon Levy Foundation, the Open Society Institute, Peter B. Lewis and John Sperling had stepped up with pledges totaling $23 million spread over the next three years. But unlike the annual Gelbaum gifts, the new money will have to be shared with state affiliates.

As can be seen at their name's link above, the ACLU works night and day to support immigration, especially of the illegal variety. And, Gelbaum has a record in that field.

In 2001, Gelbaum gave the Sierra Club a $101.5 million donation; although their Carl Pope said it didn't affect their advocacy, Gelbaum admitted this: "I did tell Carl Pope in 1994 or 1995 that if they ever came out anti-immigration, they would never get a dollar from me..."

Gelbaum might resume donating to the ACLU once the financial situation improves, but even if he doesn't don't expect the ACLU to change their ways. However, hopefully the cutbacks they'll have to make will involve that part of their operation that works to support illegal activity.