SUNNYVALE — In a rare legal move, Yahoo (YHOO) is asking a secretive U.S. surveillance court to let the public see its arguments in a 2008 case that played an important role in persuading tech companies to cooperate with a controversial government data-gathering effort.

Releasing those files would demonstrate that Yahoo “objected strenuously” to government demands for customers’ information and would also help the public understand how surveillance programs are approved under federal law, the company argued in a filing with the Foreign Intelligence Surveillance Court this week.

Yahoo’s argument against the data-gathering was rejected in a 2008 ruling that gave the government powerful leverage to persuade other tech companies to comply with similar information demands, according to legal experts. But under federal law, the court’s ruling and the arguments by Yahoo and other parties have been treated as classified information. Until last month, Yahoo was not even allowed to say it was a party in the case.

If Yahoo succeeds in unsealing some of the court files, legal experts say, it would be a historic development and an important step toward illuminating the arguments behind the controversial Internet surveillance program known as Prism, which was revealed last month by former National Security Agency contractor Edward Snowden, along with other government data-gathering efforts.

“This is the first time we’ve seen one of these companies making this broad an argument in favor of transparency in the FISA court,” said Alex Abdo, an American Civil Liberties Union attorney who works on national security issues. FISA is the acronym for the Foreign Intelligence Surveillance Act, which created the surveillance court to review and approve secret government data-gathering efforts.

Only a handful of the court’s opinions have ever been unsealed, Abdo said, although civil liberties groups have pressed for more disclosure.

“Revealing what went on in the court is critical to having a democracy,” said Jennifer Stisa Granick, a civil liberties expert at Stanford law school’s Center for Internet and Society.

In light of news reports that the surveillance court has issued broad opinions on constitutional issues in secret, Granick added, “If Yahoo is successful in revealing what the court did and why, then we will know more about the laws our government is purportedly operating under, which sadly we don’t currently know.”

Yahoo’s move is the latest effort by some of Silicon Valley’s leading Internet companies to convince the public that the companies didn’t just invite the government to peruse customer files or give authorities broad access to users’ email, Internet chats and other online activities.

Google (GOOG) and Microsoft have also challenged secrecy rules by filing lawsuits seeking permission to reveal, in broad numbers, how many requests for information they have received under national security programs.

While the companies may be legitimately concerned about customers’ privacy, they also have a strong commercial incentive, Granick noted.

“Obviously, Yahoo wants this information released because it wants users to feel that it’s trustworthy,” she said. “If Yahoo can show that it fought strenuously and really did its best to try to protect its users, that may make people feel more comfortable about Yahoo having their data.”

Experts say the 2008 case sent a strong message to other tech companies that might have wanted to resist government data requests.

“When you get presented with an order you don’t think is constitutional and the government says, ‘We have this secret court opinion that it is constitutional,’ then you are pretty much stuck,” said Mark Rumold, an attorney who has worked on surveillance court issues for the Electronic Frontier Foundation.

Yahoo was prohibited from discussing its appeal until last month, when The New York Times reported that unnamed sources said Yahoo had unsuccessfully fought the data requests on constitutional grounds.

After that news report, Yahoo persuaded the Foreign Intelligence Surveillance Court of Review, which rejected its appeal five years ago, to declassify the fact that Yahoo was the company in that case. Yahoo’s attorney, Marc Zwillinger, confirmed his involvement in the case this week.

While the court found the government’s effort was constitutional, Zwillinger wrote in a blog post, “I think there are better ways to protect the rights of U.S. persons who may be affected by this surveillance. If more of the court’s analysis, and the parties’ briefs, are made available, the public and Congress can make a more informed decision as to whether this is the program they want to have in place.”

Contact Brandon Bailey at 408-920-5022; follow him at Twitter.com/BrandonBailey.