Read somewhere that the law firm (who deals primarily with class action cases). Actually recruited some of the plaintiffs.
I am rarely home on weekday afternoons, but if I am and I turn on the tele I am shocked by how daytime TV is absolutely overrun with ads from ambulance chasers recruiting plaintiffs.
I worked with someone who did contracts for us but was a lawyer and in her off time she was going around trying to find people to join a class action against some local municipality. She said that if she got enough, she could sell the case to a big firm and let them go squeeze for a settlement. I didn't know a lawyer could sell their case to someone else (ethically) but I gather it's routine in these class action cases.