"Can We Challenge the Assertion of Tribal Court Jurisdiction?"
Answer: Yes. If sued in tribal court, non-Indian persons or entities can challenge the tribal court's assertion of civil jurisdiction in federal court. However, federal courts typically stay their proceedings to allow the tribal court to determine its own jurisdiction. Thus, before you challenge a tribal court's assertion of jurisdiction in federal court, you must first exhaust tribal remedies.
In any case, a tribal court first decides jurisdiction over non-Indian parties. If the tribal court rules that it has jurisdiction, it proceeds with the case. If the federal court later agrees that the tribal court had jurisdiction, it will not relitigate the case. Therefore, you should thoroughly present the merits of your client's case to the tribal judge, as you and your client may not have a subsequent opportunity to do so in federal court. In doing so, you should be ever mindful of the unique aspects of tribal courts described above.