The American Civil Liberties Union (ACLU), which obtained the documents through a Freedom of Information Act request, released the information on Wednesday.

In a 2009 handbook, the IRS said the Fourth Amendment does not protect emails because Internet users "do not have a reasonable expectation of privacy in such communications." A 2010 presentation by the IRS Office of General Counsel reiterated the policy.

Under the Electronic Communications Privacy Act (ECPA) of 1986, government officials only need a subpoena, issued without a judge's approval, to read emails that have been opened or that are more than 180 days old.

Privacy groups such as the ACLU argue that the Fourth Amendment provides greater privacy protections than the ECPA, and that officials should need a warrant to access all emails and other private messages.