An attempt was made at the weekend to firebomb the Suva headquarters of the Fiji Trades Union Congress.
The Daily Post newspaper says a petrol bomb with a lighted wick was thrown at the building in the early hours of Saturday morning.
But a caretaker who was alerted by the explosion managed to put out the fire before serious damage was done.
The FTUC Secretary General, Felix Anthony, described such incidents as acts of thuggery and said something similar happened during the military coups in 1987.
Police are investigating the arson attack.