Employees are always looking for ways to increase their income. One of the ways is to get a raise or a promotion within the company. Another way is to take on another job after they complete the day with you. Or maybe they have always wanted to be an entrepreneur so after working all day, they work on their own business on the side. Does your company have a policy on this?
The policy is important as it provides you with protection in case an employee moonlights with a competitor or decides to start a business that is in direct competition to you. Even if it is purely economics that is motivating the employee, what happens when they come to work tired from working additional hours elsewhere?