Earlier Wednesday morning, I posted this chart looking at the rise of government requests for user data under the Foreign Intelligence Surveillance Act. (Records of how many FISA applications were made in a given year are detailed in a periodic Justice Department report to Congress.)
But alongside the FISA search warrant is another, lesser-known form of data request called the national security letter. National security letters don't require court approval, as the kind of data they enable the feds to gather includes only basic envelope information such as phone numbers. Recipients of NSLs can challenge the order in court, just like with FISA orders.
Google recently began publishing the number of NSLs it receives from the government. Since 2009, the company has reported getting up to 1,000 such letters annually. Although Google's policy is not to hand over data unless confronted with a warrant, a federal judge ruled last month that Mountain View must cooperate with the warrantless searches compelled by NSLs.