I recently came back from Nepal and I am on H1B. I didn't have labor permit. The guy in the airport asked me if I have one and I said no. He just let me go which was nice of him. I also asked of the senior officer in the labor department if I need to get one and he told me I don't have to. That's why, I didn't bother to get one. But to be on a safe side, I advise everyone to get the labor permit.