Certain states do have laws covering employees. For instance, the state of California recently passed a law in January of 1999 that made it illegal to eavesdrop on employees in rest rooms and changing rooms or in locker rooms using video cameras. But it really vary from state to state. That's the law. E-mail is another important issue.
Employees really have a lot of freedom to monitor workers like the article says.
As the article says, it does sound like you can not expect any privacy at the workplace. Yes, there have been people who have sued their employer for violating the employee's privacy. For instance, there was a big case recently in which employees of a large hotel sued the company for videotaping in a dressing room. And the employees won. So, this, this is really broad issue of work place privacy out into the open and it's something feel very strongly about, a lot of employees think that, because there're no laws regulating what employers can do, they can really take advantage of the workers.