The Public Service Association in Tonga says it believes the government has drastically increased the fees for vehicle registration and licensing to make up for losses after the sinking of the MV Princess Ashika.
The government introduced the increases by almost 300 percent last week without prior public consultation.
The Secretary General of the PSA, Mele Amanaki, says the amount is unjustifiable but believes it's to do with the loss of the Princess Ashika ferry.
"This has cost not only the government but the people of Tonga millions of dollars. And we believe that this move by the ministry is to collect money to make up for the mistakes that they made and this is not right."
Mele Amanaki says the PSA has submitted a letter of complaint to the Acting Minister of Transport in hope of deferring the implementation of the fee increases.