Dean Summers, the head of the ITF in Australia, said the ship, the Unison Jasper, had been recently seized in Brisbane over underpayment but had been allowed to leave again after $93,000 in wages was paid to 11 Burmese crew.

Mr Summers said more paperwork had come to light showing another $60,000 at least was still owed, and so the vessel had been detained at Kooragang Island, where it just had unloaded its cargo of alumina.

"It won't be going anywhere until this is sorted," Mr Summers said.

Contacted for a response, Tomago Aluminium chief executive Matt Howell said the company "did not own or operate the ship or own its cargo".

"We are appalled at the reports of the treatment of the seafarers involved and we are working with the relevant parties to solve the problems," Mr Howell said.

He said the seamen deserved to "be treated with dignity" but the issues raised were a matter for "the vessel charterer".

He declined to comment further but as the Newcastle Herald has previously reported, Tomago Aluminium is regarded as "a tolling plant", in which each of the company's three shareholders - Rio Tinto, CSR and Norwegian aluminium company Hydro - are responsible for their individual cargoes.

It is understood that vessels such as the Unison Jasper are tendered by the individual shareholders, rather than Tomago Aluminium.

It is unclear as yet whether this happens with individual cargoes or whether the accounts are divided up later on paper, but the Herald understands the ship came from Gladstone, where Rio Tinto owns one of the city's two refineries that produce alumina from the raw material, bauxite.

Mr Summers said the vessel had been detained with the knowledge of the Australian Maritime Safety Authority (AMSA) and the Australian Border Force.

A uniformed police presence was also visible in photographs of the scene.

He understood the ship had 11 Burmese crew and nine Chinese officers.

He said COVID restrictions meant crews of cargo ships were generally unable to leave the wharf wherever they tied up and the crew of the Unison Jasper were "into their 15^th month" on board the vessel without a break.

He said the ship was flagged out of Hong Kong with Taiwanese ownership and was regarded as a "flag of convenience" vessel because it was on an Australian coastal run rather than between countries.

"This is a ship doing work that should be done by Australian seamen in the first place," Mr Summers said.

"But on top of that, the crew have been underpaid, bullied and kept in substandard conditions. This is the sort of ship where they have to buy a bottle of water if they want something to drink."

Mr Summers said the problems with flag of convenience shipping were well known but had been made even worse by COVID, because the strict quarantine rules in every port meant those on board were even more isolated than usual.

"The ship owners take their passports, they take their seamans' books, which are indespensible to these people," Mr Summers said.

"The Burmese crew are scared of the Chinese officers, too scared to speak up, and the documents mean they have them over a barrel."

The ITF works closely with its affiliate the Maritime Union of Australia.

The MUA's Newcastle secretary, Glen Williams, said there was no industrial action involved, but the union was "in solidarity" with the crew, who were all members of the Seafarers' Union of Burma.

The Herald is seeking a response from other parties involved, including Tomago Aluminium's shareholders, the representatives of the vessel, and AMSA.

We will update the story as more information comes to hand.