Internet giant Yahoo! said in a letter to users that it has received up to 13,000 requests for information from US law enforcement agencies in a six-month period ending May 31.
The letter titled "Our Commitment to Our Users' Privacy" was posted on the company's Tumbler page late Monday,
and was signed by Yahoo! CEO Marissa Mayer and the company's top lawyer, Ron Bell.
Yahoo!, along with Facebook, Microsoft and Apple, have come under heightened scrutiny since word leaked of a vast, covert Internet surveillance program by the US government, which it insists targets only foreign terror suspects and has helped thwart attacks.
Between December 1, 2012 and May 31, 2013 "we received between 12,000 and 13,000 requests, inclusive of criminal, Foreign Intelligence Surveillance Act (FISA), and other requests."
According to the letter, the most common requests "concerned fraud, homicides, kidnappings, and other criminal investigations."
"Like all companies, Yahoo! cannot lawfully break out FISA [US Foreign Intelligence Surveillance Act] request numbers at this time because those numbers are classified; however, we strongly urge the federal government to reconsider its stance on this issue."
Major Internet firms have faced a public backlash since government contractor Edward Snowden leaked details of PRISM, a vast program that saw nine high-tech companies turn over user data to the US National Security Agency.
The companies have denied claims the NSA could directly access their servers. US authorities have said the program was legal and limited.
Yahoo! said that it will issue in the next months "our first global law enforcement transparency report, which will cover the first half of the year. We will refresh this report with current statistics twice a year."
Snowden's leaks have reignited debate over the trade-offs between privacy and security more than a decade after the September 11, 2001 terror attacks in the United States.