As far as I am concerned:
If he asks you to move because he has admin things to take care of, it is fine. What I usually do is psay someone and tell them to please go to spectator so I can take care of the situation at hand. Once I take care of business, I give the slot back to the player on his/her team.
As far as admins asking you to move teams just because there friend is over there, they are not allowed to do so VIA admin. However, kindly asking someone in all chat "Would anyone like to switch teams with me?" is alright. Assuming that the admin is on the winning team and they are trying to help out the losing team, that is also fine. Admins cannot force other people to leave/join a different team. There is absolutely no rule that says you must change teams because an admin says. If there is, please point it out to me so I can learn something.