The High Court has overturned a decision that could have seen long-term casuals get leave entitlements.

The court has unanimous ruled that a casual mining worker in a test case was not entitled to backpay and leave entitlements. 

It comes after the Federal Court last year ruled in favour of casual mine worker Robert Rossato in his claim against labour hire company WorkPac.

Mr Rossato, who worked on casual contracts with WorkPac for three and a half years, was found to be a permanent worker with rights to backpay.

The landmark ruling prompted the federal government to undertake industrial law reforms on the fear that employers would be forced to spend billions backpaying casuals.

The High Court has upheld WorkPac’s appeal, saying the “the contractual arrangements between WorkPac and Mr Rossato did not include a mutual commitment to an ongoing working relationship between them after the completion of each assignment”.

The High Court found Mr Rossato's work rosters for the Glencore mine in Queensland did not establish a commitment between the parties to an ongoing working relationship after the completion of each assignment.

Australian Chamber of Commerce and Industry acting CEO Jenny Lambert said the common law practice around casual employment has been reinstated, keeping the express terms of an employment contract binding.

“The decision was a vindication for hundreds of thousands of employers who were thrown into distress and disarray by the early Federal Court decision,” she said.

The ruling is expected to support the business models of firms like Uber and Deliveroo, who have long been accused of using subcontracting as a way to distance themselves from people who might otherwise be deemed employees. 

University of Adelaide law professor Andrew Stewart said the High Court's ruling will allow companies to continue casualising the workforce.

“Today's ruling confirms that you're a casual if the contract you've signed says you're a casual – not if the work you're doing is genuinely casual in nature,” he said.

“It's an open invitation to businesses to hire workers as independent contractors rather than employees – meaning they don't just miss out on annual leave, but minimum wages, limits on working hours, the right to complain of unfair dismissal, and maybe super and workers' compensation as well.

“It will potentially open up new ways of cutting wages and working entitlements, when workers – and the economy – can least afford it.”