The Union for Exploited and Kanak Workers, or USTKE, in New Caledonia is on a 24-hour strike in response to the arrest of its leader.
Gerard Jodar has been detained over two incidents of alleged union violence.
A USTKE union spokesperson, Pierre Chauvat, says the arrest was unfair and it has called for a one-day strike as a response.
"We are today marching and rallying to ask France to apply human rights and also to defend the way that unions are struggling for the defense of the workers."
Pierre Chauvat says about 3,000 people have stopped work and are marching to the French high commission building in Noumea to show their support for Mr Jodar.