Yahoo urges US to publish surveillance order
Yahoo has called on the US government to publish a surveillance order it received so it can respond to claims it scanned its users' emails.
Earlier this month, a news report claimed the firm monitored millions of incoming messages on behalf of intelligence officials.
Chief executive Marissa Mayer was also criticised for not appealing the order.
But on Thursday, Yahoo general counsel Ron Bell called the claims "misleading" and said the order must be published.
"At Yahoo, we are deeply committed to transparency and to protecting the rights of our users," he said in a letter to US director of national intelligence James Clapper, published on Yahoo's blog site Tumblr.
"Yahoo was mentioned specifically in these reports and we find ourselves unable to respond in detail."
He asked Clapper to confirm the existence of the surveillance order, to declassify all or part of it, and to "make a sufficiently detailed public and contextual comment to clarify the alleged facts and circumstances".
The government should explain to the public the "national security orders they issue to internet companies to obtain user data," he added.
"As we've said before, recent press reports have been misleading; the mail scanning described in the article does not exist on our systems," he said.
Earlier this month, Reuters news agency said the firm built special software last year to comply with a classified request. The software allegedly scanned all Yahoo Mail users' incoming messages to isolate those containing specific data, as requested by intelligence officials.
At the time the firm told the BBC that Yahoo was "a law abiding company, and complies with the laws of the United States".
The firm said that while its letter to Mr Clapper made specific reference to the recent allegations against Yahoo: "It is intended to set a stronger precedent of transparency for our users and all citizens who could be affected by government requests for user data."
Other internet firms including Google, Twitter and Facebook said this month they had not been asked to carry out email scanning by the US government, while Microsoft said it had "never engaged" in such an activity.
US law allows the country's intelligence agencies to order the release of customer data that they believe could prevent a terrorist attack, among other reasons.
Companies can challenge such orders behind closed doors in the Foreign Intelligence Surveillance Court.