Yahoo sued Facebook on Monday over 10 patents that include methods and systems for advertising on the Web. It's the first major legal battle among big technology companies in social media.
The lawsuit, filed in a San Jose, Calif., federal court, marks a major escalation of patent litigation that has already swept up the smartphone and tablet sectors and high-tech stalwarts such as Apple, Microsoft and Motorola Mobility Holdings.
Yahoo's patent lawsuit follows Facebook's announcement that it plans for an initial public offering that could value the company at about $100 billion.
Facebook spokesman Jonathan Thaw said the company learned of the lawsuit through the media.
"We're disappointed that Yahoo, a longtime business partner of Facebook and a company that has substantially benefited from its association with Facebook, has decided to resort to litigation," he said.
In an emailed statement, Yahoo said it is confident that it will prevail.
"Unfortunately, the matter with Facebook remains unresolved and we are compelled to seek redress in federal court," the company said.
Yahoo said late last month that it was seeking licensing fees from Facebook over its patents and that other companies have already agreed to such licensing deals.