James writes, "I am employed in my country and will be visiting the United States for sightseeing for about 2-3 months. Unfortunately, my employer is allowing me to take time off but insists that I stay in touch by email/Skype a few times a week and even guide my team members when they need help. I might also need to review some documents and get some things done. I expect that it will be several hours of work each week. Is it legal for me to do so?"
It seems that as long as you are doing this work for your foreign employer and getting paid for it by them, it does not violate American laws. While visiting on tourist visa, you cannot work for an American employer and get paid. This appears to be no different than time that you could be spending chatting with your family on phone/Skype or updating your personal travel blog. It is quite understood these days that tourists will be in touch with their employment.