Is that legal? Don't they have to mail the check to the employees if they don't come in to pick it up? And why wouldn't some one pick up their check? If they are working a job like that, I imagine they need the money?
A lot of people don't know their rights, or know their rights but think they'll need a lawyer to deal with it and don't have that sort of money.
In reality a call to the Department of Labor or whatever the local equivalent is will get the money, though usually with a pretty big lag time (a threat to call the DoL can be faster).