Sforno on Exodus 23:6/ספורנו על שמות כ״ג:ו׳

1לא תטה משפט אביונך בריבו, an example of being lenient with one category of person and harsh with another. When litigants are facing you, you must not take account of any differences in their social standing. Not only this, if one of the litigants is standing during the proceedings whereas the other one is seated, this is already a form of inadmissible discrimination.