I did that a couple of years ago when a woman quit working for a friend of mine (really left her in a lurch) and took another job where she was being paid under the table. I heard through the grapevine that both she and her new employer got in some deep doodoo with the IRS. I just think people should pay their fair share of taxes, that's all. Well, that and the fact that if I don't like someone I won't hesitate to mess with them when the opportunity presents itself. But that's another thread....
Cash, if someone is working here illegally you want to contact the INS, not the IRS.