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

The threat — which was made public Thursday as part of about 1,500 pages of previously classified documents that were unsealed by a federal court — adds new details to the public history of a fight that unfolded in secret at the time, as Yahoo challenged the constitutionality of a statute that legalized a form of the Bush administration’s program of warrantless surveillance of foreigners — and lost. Under the Foreign Intelligence Surveillance Act, companies that receive data requests are prohibited by law from talking about the substance of specific requests or even acknowledging they occurred.

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 documents released on Thursday show that the government expected Internet providers to begin complying with orders under the law — which Congress later replaced with another statute called the FISA Amendments Act — before the intelligence court had approved the procedures for targeting specific accounts and protecting any private information about Americans collected incidentally in the course of the warrantless surveillance aimed at people abroad.