Feinstein pointed to statements by NSA officials that the call record collection "in combination" with other programs has helped the U.S. to disrupt terrorism about a dozen times in recent years.
Numerous lawmakers were outraged to learn that the security agency has been collecting records on millions of Americans not suspected of any wrongdoing.
Sen. Patrick Leahy, chairman of the Senate Judiciary Committee, and Rep. Jim Sensenbrenner (R-Wis.), the original author of the Patriot Act, are working on legislation to bar the NSA from collecting data in bulk.
Feinstein is working on her own bill that would increase transparency but leave the bulk collection in place.
"But we must also learn the lesson of 9/11," Feinstein wrote in the op-ed. "If we end this vital program, we only make our nation more vulnerable to another devastating terrorist attack."