Three blogs which published sensitive information about upcoming Apple products could be made to disclose where the leaks came from.
The ruling could be a blow for bloggers
A California judge said in a preliminary ruling that bloggers should not have the same protection afforded to journalists under US law.
The Electronic Frontier Foundation (EFF), representing the sites, said it was disappointed with the ruling.
The case's outcome could be far-reaching for bloggers and writers.
The civil liberties group EFF had asked California's Superior court to stop Apple pursuing the blogs' sources in February.
The tentative ruling serves as an early indication of which way the court is leaning and is not the final ruling, Annalee Newitz, EFF policy analyst, told the BBC News website.
"What's at stake here is whether online and independent journalists will be granted the same rights as ones from traditional media," Ms Newitz said.
She added that if the court's final decision stood, it would mean net service providers would be obliged to hand over bloggers' details in future legal cases.
"Given that so many journalists correspond with their sources via e-mail, this would severely undermine those journalists' abilities to guarantee their sources any kind of confidentiality," she said.
Over four months, Apple has filed against PowerPage, Apple Insider and Think Secret to find out how the websites obtained details of unreleased products, code-named Asteroid and Q97.
The EFF argued that those writing for blogs, websites which increasingly act as "unofficial" news sources, should get the same First Amendment and California Shield Law protection as journalists.
It is designed to protect journalists from being forced to reveal the names of sources or supply unpublished materials, if the matter reported is in the public's interest.
The lawsuits were filed by Apple just weeks before the MacWorld conference in San Francisco which is used to showcase new products.
Apple is famously secretive about its future product launches while Apple users are equally famous for speculating about new technology from the company.
In December 2002, Apple sued a former contractor who allegedly posted online drawings, images and engineering details of the company's PowerMac G4 computer.
Apple was not immediately available for comment.