The plaintiffs said LinkedIn was "breaking into" external email accounts, such as offered Gmail or Yahoo!, by pretending to be the account-owner, The New York Times reported.
The complaint doesn't offer details about that claim and plaintiffs' attorney Larry Russ declined to comment beyond the suit.
The lawsuit, filed Tuesday in federal court in San Jose, seeks damages on behalf of all LinkedIn users.
"As a part of its effort to acquire new users, Linkedln sends multiple e-mails endorsing its products, services and brand to potential new users," the suit said. "In an effort to optimize the efficiency of this marketing strategy, Linkedln sends these 'endorsement emails' to the list of email addresses obtained without its existing users' express consent and, to further enhance the effectiveness of this particular marketing campaign, these endorsement emails contain the name and likeness of those existing users from whom Linkedln surreptitiously obtained the list of email addresses."
The company said in a statement that LinkedIn was committed to putting members first and that the claims in the lawsuit were without merit, the Times reported Saturday.
In a blog post Saturday, LinkedIn, based in Mountain View, Calif., specifically denying it ever broken into or hacked user accounts.