Your lawyer might be right. In WA you can not hold a drawing at your booth at the county fair, because you are enticing them to "maybe" purchase. Just another law the take care of people too stupid to know that if they sign up for the drawing, that you might get a phone call about their service/product.
That being said, I'd do it anyway, I think that if someone turned you in, that you'd be lucky to get your hand slapped.