The people's committee for political reform in Tonga has launched a petition calling on the Prime Minister and his deputy to step down over last month's ferry tragedy.
Last month the Princess Ashika sank near Nomuka, claiming 74 lives.
The Public Service Association is a member of the people's committee and its secretary general, Mele 'Amanaki, says they have a copy of a letter which she says proves the prime minister knew the ferry was not fit to sail.
That document is from the Port Authority general manager, Lupeti Vi, who wrote to the Prime Minister, saying the ship was not seaworthy.
Ms 'Amanaki says he has lost the support of the public and should be removed.
"We're aware that there've been irresponsible decisions made by the prime minister and his cabinet. So we're mobilising the whole country to sign the petition to the king to put the prime minister and his deputy out of office."
Mele 'Amanaki says the petition has been published in the newspaper and delegates will visit all villages to gather support.