The International Transport Workers' Federation (ITF) has identified more than $4 million in unpaid seafarer wages in a week-long blitz of ports along the New South Wales coast.
The operation was part of the ITF's Nowhere to Hide campaign and included inspections on 77 foreign-owned vessels at Port Kembla, Newcastle and Sydney.
ITF's Australian deputy coordinator Matt Purcell said many ships around Australia had exploited workers on them.
"You can't see it, it's out of sight, out of mind. It's the most unregulated industry in the world - some of these ship owners do what they like," Mr Purcell said.
ITF's Australian coordinator Ian Bray said the inspectors uncovered an incredible amount of money owed to workers in the short time.
"We recovered 20 back payments of $749,860, and in back pay pending ... we identified $200,000," Mr Bray said.
Under the Commonwealth Coastal Trading Act, foreign ships are entitled to two voyages at lower rates of pay. When the vessel makes any additional trips, Australian wage standards apply.
"We recovered $95,622 in coastal pay and we identified, and it is pending, $3,000,070 [in] potential coastal trading payments," Mr Bray said.
"Australian award doubles their wage per month, so it is [an] 100 per cent pay increase just to get the minimum conditions acceptable to the Australian community."
Mr Bray said another area of "inadequacy" in the law saw ships trading on the coast but on a ballast run, where they were not carrying cargo, and crew's wages were "stripped back to international rates".
"If you're on the coast and you are working here, you should be treated no different, it should be the award [pay]," he said.
The inspections also helped three seafarers receive medical assistance, ensured additional provisions were provided to three ships, secured shore leave for two crews and identified one abandonment claim.
In addition, Mr Bray said the inspections secured six repatriations.
"These are people who have been in isolation for a long time and for some hope is lost," he said.
Prior to this week, the ITF had conducted 305 inspections and recovered more than $7 million.
German ITF inspector and coordinator Sven Hemmer said the situation for many seafarers was "modern-day slavery".
"They all complain that they are alone, they are far away from their families, many ship owners still don't pay for free internet access for the crew so it is hard for them to stay connected," Mr Hemmer said.
"They earn little money; they spend what little money they have to pay for internet access just to have the connection back home and make it easier to survive the nine to 10 months away."
Mr Hemmer said the majority of seafarers came from the Philippines, India, China, Myanmar, Ukraine and Russia.
"They don't do it because they have a romantic picture of a seafarer's life, they do it because they need to earn money for their families and sometimes entire villages," he said.
He said base international rates of pay were between $US1,100-$1,400 a month.
"It is the most isolated job in the world as you spend nine to 10 months in a steel shell, working 12-14 hours a day, seven days a week," he said.
"It's exhausting and causing mental health concerns."
Malaysian ITF inspector Hakimah Saiful Bahri was also involved in the week-long operation.
"The inspections are critical and let seafarers know about the Seafarers' Bill of Rights, explaining their salary and conditions," she said.
A seafarer of 13 years before becoming an inspector, she said the monetary benefits were
"worth the sacrifice" when income was hard to find at home, especially in developing countries.
She said more women were now looking at the career.
"It is very good to see a female face on board a ship ... it's important to ensure the women have support from other women," she said.
Mr Bray urged the boards of major companies using ports in Australia to look at how they could "mitigate risk to reputation" by vetting for human rights in their reporting procedures.
"They vet ships for safety, insurances, cargo capacity but one of the things they have been lacking on is the human rights capacity," he said.
"If they included that into their vetting systems, I reckon that would make a vast improvement to the industry in terms of the amount of exploitation and helping to avoid modern slavery."
He said the ITF was eagerly awaiting the federal government meeting its to secure essential supplies for Australia in emergencies.
"Securing Australia's sovereign risk and providing a baseline to stop exploitation, that will help reset standards for the international fleets," he said.