The U.S. government once threatened to fine Yahoo $250,000 a day if it failed to assist with its surveillance efforts, Yahoo said Thursday.

Yahoo said it was threatened with the fines after it challenged surveillance powers granted to the U.S. government under the Protect America Act of 2007. The information has come to light now because the Foreign Intelligence Surveillance Court, which oversees how those laws are implemented, agreed to unseal documents in the case.

Yahoo said it was "extremely rare" for the court to make such records public. It highlighted some of their contents in a blog post and said it would soon post the 1,500 pages of unsealed documents online.

"We consider this an important win for transparency," Yahoo General Counsel Ron Bell said in a blog post.

Yahoo said it challenged the surveillance request on the grounds that it was unconstitutional and overly broad. But it failed in its bid and was ordered by the court to hand over data about its users.

The government was looking to collect "foreign intelligence information" about "targets reasonably believed to be located outside the United States," the Office of the Director of National Intelligence said in its own blog post. The court said it was acceptable for the surveillance to include U.S. citizens if they were outside the country.

Documents leaked last year by former National Security Agency contractor Edward Snowden detailed sophisticated surveillance methods used by the U.S. government to gather data held by online companies including Yahoo, Google and Microsoft. One of the programs, dubbed PRISM, claimed the NSA was tapping into companies' servers, according to those documents.

The high-tech firms have sought to emphasize their efforts to fight the government data requests and reject any suggestion that they participated willingly in the information gathering.

Zach Miners covers social networking, search and general technology news for IDG News Service. Follow Zach on Twitter at @zachminers. Zach's e-mail address is zach_miners@idg.com