Police in New Caledonia have surrounded the headquarters of the USTKE union in Noumea after its leader, Gerard Jodar, failed to appear for questioning over last month's clashes.
All vehicles entering and leaving the site are being checked as union supporters have set up barricades with tarpaulins and tyres.
The prosecutor says two summons were sent to Mr Jodar but he says he hasn't received any of them and has no intention of being questioned.
Mr Jodar says he is awaiting the arrival of his lawyers.
Several USTKE members are in jail as investigations continue into the violence which erupted amid a strike at a bus depot.