Senator Ron Wyden is asking the Attorney General Merrick Garland to disclose information on the AT&T Hemisphere surveillance program.

Senator Wyden is a well-known privacy advocate, routinely putting pressure on companies and lawmakers to do more in the interests of protecting user privacy. In a letter to AG Merrick, Senator Wyden raised concerns about Hemisphere, a program that gives “federal, state, local and Tribal law enforcement agencies” the ability to search trillions of AT&T phone records as far back as 1987.

Under the Hemisphere program, the White House Office of National Drug Control Policy (ONDCP) indirectly pays AT&T to allow any federal, state, local or Tribal law enforcement agency to search AT&T customers’ phone records as far back as 1987, according to public records about the program.

“I have serious concerns about the legality of this surveillance program, and the materials provided by the DOJ contain troubling information that would justifiably outrage many Americans and other members of Congress,” Wyden wrote. “While I have long defended the government’s need to protect classified sources and methods, this surveillance program is not classified and its existence has already been acknowledged by the DOJ in federal court. The public interest in an informed debate about government surveillance far outweighs the need to keep this information secret.”

Although information regarding Hemisphere is not classified, it is marked as “Law Enforcement Sensitive,” which is enough to keep it the information out of the public. What’s more, Senator Wyden’s office says the program has not been subject to a federal Privacy Impact Assessment.

Rather than directly funding the surveillance program, the ONDCP provides a grant to the Houston High Intensity Drug Trafficking Area, a partnership between federal, state and local law enforcement agencies, which in turn pays AT&T to operate this surveillance program. Law enforcement agencies nationwide are able to request Hemisphere searches, including for investigations that are not drug related, Houston HIDTA officials told Wyden’s office.

US government agencies have increasingly turned to purchasing information from companies instead of going through the trouble to getting a warrant. The Hemisphere program may be one of the biggest such examples, which would explain Senator Wyden’s concern.