I was told in an answer to one of my questions that in Shulchan Aruch Hoshen Mishpat 188:1) it says Jew cannot be the agent of a non Jew and I saw it again in this schul handout below.
What is the scope of this invalidity (I.e. Not an agent for things involving an issue or halachic change but ok for business) and what is the derivation of this halacha?