The pro-independence Caledonian Union has urged its members not to sign off the electoral lists being finalised by special committees this week.
This comes amid sharp disagreements over who is eligible to vote in next month's provincial election, whose outcome is seen as crucial for a possible independence referendum.
The pro-independence FLNKS movement has demanded that more than 6,000 names be struck off the roll for failing to meet the residency terms under the 1998 Noumea Accord.
The special committees, which include local political parties and French judges, have refused to remove names, prompting the FLNKS to take urgent legal action.
The tribunal has vetted the cases last week and decisions are being sent out.
The Caledonian Union says the challenges have been thrown out, which it says amount to a denial of justice.