Tight security is in place in New Caledonia as the appeal court is hearing the case of 28 unionists convicted in connection with the skirmishes at Noumea's domestic airport in May.
Six of those sentenced have been in jail since late June, including the USTKE union leader Gerard Jodar.
Radio New Caledonia says access to the court premises has been restricted by police as tension has been high after last month's violent protests in a unsuccessful bid by the union to win the release of its members.
The USTKE campaign was denounced two weeks ago in the biggest rally the territory has seen in decades only to be followed by a counter march decrying alleged police brutality.
The incident at the airport emanated from a minor labour dispute with the domestic airline.