EFF and other civil liberties groups filed an amicus brief in Warshak v. United States urging the 6th U.S. Circuit Court of Appeals to hold that the government's seizure of email without a warrant violated the Fourth Amendment and federal privacy statutes as well as the Justice Department's own surveillance manual.

During its criminal investigation the Department of Justice illegally ordered defendant Stephen Warshak's email provider to prospectively "preserve" copies of his future emails which the government later obtained using a subpoena and a non-probable cause court order. The government accomplished this "back door wiretap" by misusing the Stored Communications Act (SCA) which is only supposed to be used for obtaining emails already in storage with a provider.

EFF filed a similar amicus brief with the 6th Circuit in 2006 in a civil suit brought by Warshak against the government for its warrantless seizure of his emails. There the 6th Circuit agreed with EFF that email users have a Fourth Amendment-protected expectation of privacy in the email they store with their email providers though that decision was later vacated on procedural grounds.