The threat — which was made public Thursday as part of about 1,500 pages of previously classified documents that were unsealed by a court — sheds a rare spotlight on the fight between Internet companies and the government over the ground rules for the secret surveillance of Americans and foreigners following the 9/11 terrorist attacks. Under the Foreign Intelligence Surveillance Act, companies that receive data requests are prohibited from talking about the substance of the interactions or even acknowledging they occurred.

NEW YORK — The federal government was so determined to collect the Internet communications of Yahoo customers in 2008 that it threatened the company with fines of $250,000 per day if it did not immediately comply with a secret court order to turn over the data.


Yahoo’s 2008 challenge to the warrantless surveillance law and an appeals court’s rejection of that challenge were first reported by The New York Times last year, shortly after Edward J. Snowden, a former National Security Agency contractor, exposed a more extensive government surveillance program called Prism through classified documents leaked to the Washington Post and the Guardian.

The court documents released Thursday show that Yahoo was forced to comply with the order to turn over data even though the government and the appeals court had yet to set out clear rules to minimize the amount of data collected from Americans, who were supposed to have special protection under the law, which was principally aimed at foreigners.

The records also provide perhaps the clearest corroboration yet of the Internet companies’ contention that they did not provide the government with direct access to vast amount of customer data on their computers.

When the Snowden revelations surfaced last summer, there were reports that the government had direct access to query the databases of Internet companies for any information they wanted — a claim that the Internet companies have consistently denied.


Instead, they said, the government had to send them a lawful request for informa- tion on a specific individual and only then would they hand it over.

In a document reporting on its compliance with the 2008 order to turn over customer data, the company said it had begun surveillance on the requested accounts, beginning with the government’s highest-priority targets.

That indicates the government was sending Yahoo the names of the people it was investigating and waiting for Yahoo to send the information, as opposed to directly accessing Yahoo’s servers.

Overall, the cache of documents shows how Yahoo fought the government and eventually lost its appeal. That helped to set the stage for a vast expansion of the federal government’s surveillance of Internet users through the secret Prism program.

Ultimately, Yahoo and seven other companies, including Google, Facebook, Apple, and Microsoft, agreed to provide data to the government.

Yahoo described the government’s threat to seek fines in a blog post on Thursday. A Yahoo spokesman further explained that the court ordered the company to comply while its appeal was pending.

Proceedings in front of the Federal Intelligence Surveillance Court are usually secret, and Yahoo had been pressing for months for the declassification and release of the case documents.

Material from the Washington Post was used in this report.