Shulchan Aruch(C.M. 26:1): It is prohibited to have a non‑Jewish
court make judgments in a dispute between Jews. This is so even
if they make judgments based on Jewish law and even if the
litigants agree to accept their judgment. Who ever used the
non‑Jewish court is a rasha (wicked person). It is as if he has
denigrated the Torah of Moshe. Rema: The Jewish court has the
right to excommunicate and ostracize those who utilize the
authority of non‑Jews. Similarly there can be various
punishments enacted against someone who goes to a non‑Jewish
court – until they retract…. Shulchan Aruch(C.M. 26:2): If the
non‑Jews are the controlling power and the litigant is powerful
in his own right and therefore the person can not recover what
is his by the authority of the Jewish court – he should first
summon his opponent to the Jewish court. If his opponent refuses
to go – he should obtain permission from the Jewish court and
then use the non‑Jewish court to recover what is his from his
opponent. Rema: The Jewish court ha