Privacy experts and digital rights advocates want the House of Representatives to reform a loophole to National Security Agency surveillance authority set to expire in December that allows the intelligence community to collect and search data on U.S. citizens without a warrant.

The American Civil Liberties Union (ACLU) in a Tuesday letter called on the House Judiciary Committee to close that loophole in legislation the committee is drafting to reauthorize Section 702 of the 2008 Foreign Intelligence Surveillance Amendments Act (FISA). Section 702 lets the NSA surveil without a warrent foreign nationals communicating with U.S. persons. Critics say it sweeps up data on potentially tens of millions of Americans, which the intelligence community can search under the pretext of national security.

Attorneys for the ACLU said the reform that House lawmakers are considering “would leave the so-called ‘backdoor search loophole’ wide open.”

“We urge you to ensure that any reform proposal include a full fix requiring all agencies to obtain a warrant based on probable cause to search Section 702 data for information about U.S. citizens and residents in all investigations,” reads the letter, signed by a bipartisan group of privacy and digital rights advocates including the Electronic Frontier Foundation, New America’s Open Technology Institute, and the R Street Institute.

Section 702 lets the NSA tap the physical infrastructure of internet service providers, like fiber connections, to intercept foreign emails, instant messages, and other communications belonging to foreign nationals as those messages exit and enter the U.S. According to the NSA it also “incidentally” sweeps up the communications of Americans corresponding with, and until recently, merely even mentioning foreign targets.

Though the law forbids targeting persons inside the U.S., intelligence agencies including NSA, CIA, FBI, and others report they search the incidentally-collected data “in broadly defined ‘foreign intelligence’ investigations that may have no nexus to national security, in criminal investigations that bear no relation to the underlying purpose of collection, and even in the pre-assessment phase of investigations where there are no facts to believe someone has committed a criminal act” absent any warrant requirement, according to the ACLU.

While House lawmakers haven’t released any details about the bill, the New York Times reported in September the proposed legislation would require “FBI agents obtain warrants before searching the program’s repository of intercepted messages for information about American criminal suspects.” The Hill later reported “investigators would apparently only be required to seek a warrant to use Americans’ data in criminal investigations, not national security investigations.”

Lawyers for the ACLU say a “warrant requirement only to searches of Section 702 data involving ‘criminal suspects,’ is not an adequate solution to this problem,” and “ignores the fact that the Fourth Amendment’s warrant requirement is not limited to criminal or non-national security related cases.”

“[U]nder traditional FISA, agencies wishing to collect Americans’ communications in foreign intelligence investigations are required to apply to the FISA Court for an individualized warrant,” the letter said. “Warrantless searches of Section 702 data thus undermine constitutional protections and create an unacceptable loophole to access Americans’ communications in criminal and foreign intelligence investigations alike.”

According to the ACLU, limiting warrant reform to only “criminal suspects” would “likely exclude thousands of searches by the NSA, CIA, and FBI that target U.S. citizens and residents” and “exclude searches performed by the NSA, CIA, and [the National Counterterrorism Center],” agencies focused on foreign threats. The CIA and NSA report they performed 30,000 searches for information about U.S. persons in 2016 alone.

Neema Singh Guliani, legislative counsel for the ACLU, said Thursday that if Congress can’t “significantly reform Section 702, including by completely closing the ‘backdoor search loophole,’ then they should allow the law to sunset” at the end of December.

“Federal agencies like the NSA and FBI should not be permitted to conduct tens of thousands of searches targeting people in the U.S. without a warrant based on probable cause,” she said. “Furthermore, any fix that includes broad national security or intelligence loopholes fails to adequately protect activists, government critics, and minority communities that have a history of being improperly surveilled.”

Attorney General Jeff Sessions and Director of National Intelligence (DNI) Dan Coats asked the leaders of both parties in the House and Senate to permanently reauthorize Section 702 without reform in September. That scenario seems unlikely based on opposition to the law on both sides of the aisle.

Democrat Sens. Ron Wyden of Oregon and Al Franken of Minnesota have blasted intelligence officials for repeatedly failing to produce an estimate of how many Americans are swept up in Section 702. Republican Sen. Rand Paul of Kentucky has raised similar concerns while Republican Sen. Lindsey Graham of South Carolina has taken issue with Section 702 potentially being used for political targeting when used to surveil government leaders in contact with foreign officials, as happened to former National Security Adviser Michael Flynn with Russian Ambassador Sergey Kislyak.

Sessions and Coats in their own letter to Congress argued the program is subject to rigorous oversight from Congress and the Foreign Intelligence Surveillance Court, which oversees the intelligence community in secret. They reiterated Section 702 is not intentionally used to surveil Americans.

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