The president of New Caledonia's USTKE union, Gerard Jodar, has been detained in connection with investigations into two incidents of alleged union violence.
According to the public prosecutor, Mr Jodar and four others had failed to respond to summons.
Union members are alleged to have assaulted a court official outside a construction company that has been shut by a union blockade.
The other incident relates to unionists allegedly assaulting two police officer during a visit to Noumea by the French overseas territories minister, Christian Estrosi.
The USTKE union has labelled the arrests as a criminalisation of union activities.
In response, the USTKE union has called for a general strike.