Yahoo is the latest company to reveal its dealings with the US authorities, following revelations about the Prism surveillance programme.
It said it had received between 12,000 and 13,000 US government requests for user data in the past year and a half.
Most of them had "concerned fraud, homicides, kidnappings, and other criminal investigations", it said.
Yahoo voiced frustration that it was unable to reveal the number of requests that had concerned national security.
It urged the government to "reconsider its stance on this issue".
"Like all companies, Yahoo cannot lawfully break out Fisa [Foreign Intelligence Surveillance Act] request numbers at this time because those numbers are classified," it said in a blog post by chief executive Marissa Mayer and general counsel Ron Bell.Yahoo Declares Its Commitment To User's Privacy, In Wake of PRISM [bbc.co.uk]