In May 2011, Ms. Callahan and Ms. Schlanger raised their concerns with the chief of their agency, Janet Napolitano.

WSJ: U.S. Terrorism Agency to Tap a Vast Database of Citizens

Ms. Schlanger returned to her faculty position at the University of Michigan Law School soon after but remains an adviser to Homeland Security.

WSJ: U.S. Terrorism Agency to Tap a Vast Database of Citizens

"I'm not sure I'm totally prepared with the firestorm we're about to create, " Ms. Schlanger emailed Ms. Callahan in November, referring to the fact that the two wanted more privacy protections.

WSJ: U.S. Terrorism Agency to Tap a Vast Database of Citizens