Australia's The Age newspaper reports five workers are suing Agri Labour in the Federal Court for $US7.4 million.
They allege gross underpayment and mistreatment.
The paper reported Agri Labour was suspended from bringing new workers to Australia under its Seasonal Worker Programme after revelations 50 workers from Vanuatu had worked in shocking conditions on a farm near Shepparton, earning under $US6 an hour.
The Fair Work Ombudsman has also launched an investigation.
The Brisbane-based labour hire firm Agri Labour has strongly denied the allegations levelled against it as "false".
The Age reported in the legal claim, one of the workers Tulia Roqara alleged she was underpaid by US$8,140 for four months work through underpayment and unlawful deductions from her pay by Agri Labour.
Agri Labour's Casey Brown said his company was cooperating fully with investigations into its conduct and described claims against it as false.