Poorly-trained crews struggling to survive aboard rust-bucket vessels on the high seas also posed severe environmental dangers to natural wonders such as the Great Barrier Reef, the report found.
The Ships, Slaves and Competition report, released by the International Commission on Shipping (Icons), found up to 15 percent of international shipping firms failed to comply with global safety standards.
"For many thousands of seafarers today, life at sea is modern slavery and their workplace is a slave ship," Icons chairman Peter Morris said.
He called on the Australian government to conduct tighter reviews of suspect vessels attempting to enter Australian waters, and for a more stringent ethical response from private sector exporters.
Global resource sector heavyweights such as BHP and Rio Tinto, the world's biggest mining company, should refuse to use shipping companies suspected of flouting safety and international labour laws, he said.
Morris presented the report to the Asia Pacific Economic Co-operation forum's international symposium on maritime safety in Sydney.
During the year-long investigation, Icons received 125 written submissions and held public meetings in both First and Third World port cities around the globe, including Sydney, Manila, London and Mumbai.
Morris said the worst abuses on the high seas included: "Delayed or non-payment of wages, denial of adequate food and accommodation, denial of medical treatment and rest time, physical and psychological abuses, sexual assault and abandonment."
"There is a need for absolute vigilance to ensure that those ships do meet all the international safety requirements," he said.
"You saw one recently with the Bunga Teratai Satu sitting up on the Barrier Reef - a new ship with all the best gear on board," Morris said in relation to the Malaysian-owned cargo ship that became grounded on the World-Heritage listed site late last year.
"If you're going to have a Mercedes, you need to know how to drive it." - Sapa-AFP