Yosef Karo, Shulchan Aruch — Choshen Mishpat 26
“ Anyone who is judged in front of them is wicked and it is as if he blasphemed, rebelled and lifted his hands against Toras Moshe. The Jewish court has the power to put a nidui and cherem on him until he removes the case against his adversary from the secular court. We similarly put a cherem on anyone who goes to a gentile, even if it is not to be judged, but just to have him force his adversary to a Jewish court. It is appropriate to lash him on the pillar. See later Siman 388 with respect to someone who goes to a secular court and is found liable and then comes in front of a Jewish court. ”
