Abaye found Rav Yosef engaged in compelling [the writing of] bills of divorce. He said to him: We are laymen [not formally ordained judges of the original tradition], and it has been taught: Rabbi Tarfon used to say: Wherever you find heathen tribunals, even though their law is like the law of Israel, you are not permitted to resort to them, as it is said, "And these are the ordinances which you shall set before them" (Exodus 21:1) - before them [Israel], and not before heathens.
Why Israelite Disputes Belong Before Israelite Courts
Yalkut Shimoni on Torah 308:2
אַבַּיֵּי אַשְׁכַּח לְרַב יוֹסֵף דַּהֲוָה קָא מְעַשֵּׂי אֲגִיטֵּי, אֲמַר לֵיהּ, אֲנַן הֶדְיוֹטוֹת אֲנַן, וְתַנְיָא, הָיָה רַבִּי טַרְפוֹן אוֹמֵר, כָּל מָקוֹם שֶׁאַתָּה מוֹצֵא אֲגוֹרִיָּאוֹת שֶׁל כּוּתִיִּים, אַף עַל פִּי שֶׁדִּינֵיהֶם כְּדִינֵי יִשְׂרָאֵל, אִי אַתָּה רַשַּׁאי לִזָּקֵק לָהֶם, שֶׁנֶּאֱמַר וְאֵלֶּה הַמִּשְׁפָּטִים אֲשֶׁר תָּשִׂים לִפְנֵיהֶם, וְלֹא לִפְנֵי כּוּתִיִּים.