New Caledonia's court of appeal has decided to keep the USTKE union leader Gerard Jodar in jail at least until mid September when it will release its verdict.
Jodar was jailed in June for a year in connection with the skirmishes at Noumea's domestic airport in May.
He and 27 others were in the appeal court on Tuesday in a bid to have their sentence thrown out.
The hearing took place amid tight security with access to the court premises restricted by police.
This followed 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.