Kissandra Cohen, a former paralegal, alleges Brockovich, along with attorney Edward Masry and celebrity private eye Anthony Pellicano, illegally taped her conversations at the time she was involved in litigation against Masry, her former boss.
Cohen's lawsuit, filed earlier this month in Los Angeles Superior Court, says she learned about the wiretaps from the FBI in 2002 after a jury ordered Masry to pay Cohen $120,000 for slander.
Masry and Brockovich did not return phone calls seeking comment Monday.
Pellicano's attorney, Victor Sherman, dismissed the allegations, saying: "I guess people will come out of the woodwork to say anything."
Pellicano, sentenced in January to two and a half years in federal prison for possessing firearms and explosives, remains the subject of an investigation into whether he illegally wiretapped celebrities.
Brockovich, an investigator with Masry's law firm, rose to prominence when she put together a landmark 1996 water pollution case that won the residents of the small desert town of Hinkley a $333 million settlement from Pacific Gas and Electric Co.
The story of that case was told in the movie "Erin Brockovich," which earned Julia Roberts a best-actress Oscar.