A California judge said in a preliminary ruling that bloggers should not have the same protection afforded journalists under US law.
The Electronic Frontier Foundation (EFF), representing internet sites, said it was disappointed in the ruling. The case could have far reaching consequences for bloggers.
EFF had asked California's Superior Court to stop Apple from pursuing bloggers and their sources in February. The ruling serves as an early indication of which way the court is leaning and is not a final ruling, according to EEF analyst Annalee Newitz.
She added that if the court's final decision stood, it would mean that internet service providers would be obliged to hand over bloggers' details in future legal cases.