Is it unethical to hire students for private consulting work?

As a faculty member, I tend not to involve students in any of my own consulting projects, but I often run into small units of work that would be great opportunities for students, especially undergraduates. Is it unethical for a faculty member to employ students as consultant for private, non-academic projects? I can see how many students may find such opportunities valuable, but I am curious about ethical issues that such a relationship might introduce.