The Tonga Customs Department has confirmed that more than 20 boxes of mostly frozen goods have been seized from a container vessel.
The confiscated goods are mostly perishable food items but also include cans of peaches, and tyres.
Radio Tonga reports Customs officials witnessed the allegedly illegal unloading of the goods at sea from the Saint Theresa to another vessel, Princess Royal.
The goods were then confiscated.
The Minister responsible for Customs, Fe'ao Vakata, says he has been told that the engine of the Saint Theresa had broken down, prompting the removal of the goods to another vessel.
But he says the ships' skippers had not followed the correct procedure.