1)    It is forbidden to steal or rob even the smallest thing or amount, be it from a Jew or a Non-Jew. It once happened that a Jewish man swindled a Non-Jew when measuring out the things he was selling to him, and with the profits he bought a jug of oil, and he was punished for this that the jug broke and the oil was spilt. (Kitzur Shulchan Aruch 182)

2)    In one way stealing from a Non-Jew is more severe than stealing from a Jew, as a Non-Jew will definitely not forgive or forget. Furthermore, by doing this he causes damage in the upper spheres as the angel appointed over that Non-Jew will steal the heavenly influences which had been granted to that Jew, in direct return for that which the Jew did. It follows that one must be very careful about this. (Ben Ish Chai Ki Setzei)