If a stranger, someone of foreign origin, resides with you in your land, you must not mistreat him.
Do not cause him distress through hurtful comments, by cheating him, or in any other manner.
Obviously it is prohibited to mistreat any person.
However, since a stranger is unprotected and unfamiliar with local customs, there is greater opportunity, or even temptation, to upset, mock, or otherwise demean him.
–Rabbi Adin Steinsaltz
Leviticus 19:33 of the Steinsaltz Chumash