Facebook Inc. may rake in more than $18 billion in its initial public offering. And plaintiffs lawyers are already vying for a big chunk of the proceeds: Plaintiffs in a proposed privacy class action filed an amended complaint Thursday in San Jose federal court demanding $15 billion in damages and injunctive relief.

The suit claims Facebook improperly tracked users’ activity between May 27, 2010, and Sept. 26, 2011, even after they logged out, in violation of federal and state laws.