That depends on the company that they work for - most companies strongly discourage moonlighting as it opens them up to liability should your side work fail and you get sued.
In lawsuits, generally, the deep pockets get the most attention so your home company would be a target, even if they had nothing to do with your side design.
Legally, if its OK with your company to do this (which I doubt) in the US, its not outlawed.
Keep in mind, that if you work on the side, you also do not have your companies corporation to shield you from lawsuits. Got any insurance of your own?
In Ontario it is included in the code of ethics that moonlighting is allowed as long as your primary employer is informed of it. If you do it without letting your employer know then it is against the law.
Moonlighting can be good for the pocketbook but it very rarely makes for a comfortable situation at work. I did it a few years ago and my employer was fully aware of the fact.
When I went to work for them, they knew me as a local design source whom they had used in the past so they were aware of the fact that I had work from several sources.
However, things changed in the course of time and the volume of work that they had demanded all my time but all it would take was for me to get behind a little and you could actualy feel the suspicions that I was not giving their work my full attention. I even heard a rumor that I was being suspected of moonlighting on their time.
Another thing that cropped up was if I took a day or two off for some reason, there was actualy some hinting that I was out drumming up more work.
All in all, I think the person who hired me had'nt given it enough thought and it didn't make for a pleasant atmosphere so I left the company.
