In June 2013, The Guardian published a classified document leaked by former intelligence contractor Edward Snowden detailing how the NSA is vacuuming up call data from the Verizon phone network under the auspices of Section 215 of the Patriot Act. Within days, the ACLU filed a lawsuit against the Director of National Intelligence James Clapper to defend Americans' rights to privacy, due process, and free speech.

EFF is separately litigating multiple cases over NSA spying, but EFF has also filed amici briefs to support the ACLU's lawsuit. At the district court level, EFF represented Rep. Jim Sensenbrenner, one of the original authors of the Patriot Act, who told the court that the NSA's mass telephone records collection program was not what Congress intended when it passed the legislation. At the appellate level, EFF represented 17 computer scientists and professors, who explained that telephone call metadata can reveal behavioral patterns of innocent Americans, including their political and religious affiliations. 

On May 7, 2015, the U.S. Court of Appeals for the Second Circuit ruled in favor of the ACLU, finding that "the telephone metadata program exceeds the scope of what Congress has authorized and therefore violates [Section 215]." On October 29, 2015, the Second Circuit remanded the case back to district court.