Democratic Sens. Ron Wyden of Oregon and Mark Udall of Colorado say Director of National Intelligence James Clapper has failed to justify the National Security Agency’s massive collection of phone data, and are troubled that Clapper did not rule out collecting cell phone location data.

The two senators released a letter from Clapper responding to a series of questions from senators about NSA programs and activities.

“Given the implications for the privacy of the millions of law-abiding Americans, intelligence leaders were specifically asked to demonstrate the unique value of the bulk phone records collection program,” Udall and Wyden said in a joint statement. “They did not.”

The two senators take particular note of Clapper saying there are no current plans to use cell phone tower location data to track the whereabouts of U.S. persons.

“It’s also deeply troubling that while the NSA claims no current plans to turn Americans’ cell phones into tracking devices, it clearly claims the authority to do so. This response leaves our question of past plans unanswered,” Wyden and Udall said.

The public version of Clapper’s response indicates Congress would be notified of changes on that subject, with further details available in a classified attachment.

The unclassified letter from Clapper is available here.