The seven justices of the High Court found unanimously in favour of WorkPac, but one of them - Hunter-born Justice Stephen Gageler - wrote a supplementary judgement explaining that recent legislative changes by the Morrison government defining "casual" employment had "stripped" the two Federal Court decisions of "precedential effect", meaning yesterday's decision would have "significance for few other than the parties" involved.

Justice Gageler said the parties had agreed a casual worker lacked "a firm advance commitment" for future work but that they disagreed how this was defined. If it was necessary to resolve this point he would have "felt the need to give greater attention" to the issues, but it was not, so he did not.

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Justice Gageler said he agreed with the other judges that there was "nothing to oblige WorkPac to continue each contract of employment beyond completion of the assignment to which each contract related". This was enough for him to find there was no commitment of "indefinite" work for Mr Rossato.

"He was a 'casual employee'," Justice Gageler wrote.

The Rossato cases and others like it - including the Adero Law class action headed by former Mount Arthur Chandler Macleod "casual" Simon Turner - began because coal casuals were earning substantially less than directly employed mineworkers in the Hunter and Queensland.

Another set of cases between WorkPac and Queensland coal truck driver Paul Skene have also been part of the picture.

Adero principal Rory Markham said the Rossato decision was a setback but his firm was still looking at pushing ahead with its cases.

Employer groups feared the precedents set in Rossato and similar case would flow into the broader workforce, where casual workers were supposedly paid substantially more per hour than the permanent rate - the casual "loading" - to make up for annual leave and other entitlements.

Coal industry employers also claimed to be paying 25 per cent loadings but as the Newcastle Herald has repeatedly reported, the Mining and Energy Union and others have shown mining casuals with take-home pay typically 40 per cent lower than permanents, and with no leave entitlements.

This message was taken up yesterday by Federal Labor industrial relations spokesperson Tony Burke, who said the High Court's "disappointing" decision was backed by the Morrison government, which had joined WorkPac in the case and passed laws "extinguishing the rights" of casual workers.

"A Labor government will overturn the government's scheme, ending the rorts and restoring rights to workers," Mr Burke said.

"If workers want to be casuals they can be. But in our meetings with mine workers throughout Queensland it's clear many casual workers want the security, pay and conditions of the permanent workers doing the same job beside them."

Mr Burke said the Coalition government spent hundreds of thousands of dollars joining the Rossato case "to ensure casuals can be ripped off".

The Herald has reported that government contracts available for public scrutiny indicate that the government and the public service is one of the biggest users of labour hire in Australia.

This was revisited recently in Senate estimates hearings, when the NDIA confirmed it had more than 1500 labour hire employees on its books. Veterans Affairs was also using labour hire. Both the NDIA and Veterans' Affairs mentioned public service hiring freezes in their evidence.

The Mining and Energy Union's general president, Tony Maher, said the Morrison government's March legislation, passed with the help of One Nation, "embedded an unfair definition of casual in the Fair Work Act and blocked pathways to compensation".

Australian Industry Group chief executive Innes Willox said the Fair Work amendments helped avoid potential employer payouts of $40 billion if the Federal Court rulings were allowed to stand, but yesterday's verdict was still important.

"It's time for all political parties to move on and to support the sensible reforms that have already been legislated for, rather than proposing changes to the definition of a 'casual employee' in the Fair Work Act," Mr Willox said.

He also called on law firms backed by litigation funders to withdraw their various class actions, which had been "exceptionally disruptive for employers".

ACTU secretary Sally McManus said the Rossato outcome was "yet another blow for many hard-working Australians, who have nothing left to give after 18 months of economic hell".

"Workers across the country are struggling with no paid leave entitlements, no confidence about where their next shift is coming from and no job security," Ms McManus said.

"Insecure work is making it harder than ever for families to make ends meet. For example, casuals employed in mining are paid $30 per hour less than their permanent co-workers, and still they have no rights to paid sick leave or holidays.

"Instead of fixing this situation, earlier this year Scott Morrison passed new laws to make it harder for workers to secure permanent jobs, giving the green light to rampant casualisation, rolling out the red carpet to dodgy labour hire operators and making a bad situation even worse."

The Australian Mines and Metals Group also applauded the verdict, with its chief executive Steve Knott saying "common sense had finally prevailed".

"The uncertainty in this area stretches back to 2016 when the Federal Circuit Court first flipped the common understanding of casual employment on its head in the Skene matter," Mr Knott said.

"This was compounded by similar findings of the Full Federal Court in Rossato.

"The damage these decisions have had on business confidence in just about every sector of the economy has been enormous. The view from the employer community has always been that the Federal Court was applying a highly novel interpretation that was out-of-step with how casual employment arrangements have worked in practice for many decades.

"While it is disappointing WorkPac had to take the Rossato matter all the way to the High Court, employers strongly welcome the confirmation that the Federal Court had erred in its interpretations."

HIGH COURT OF AUSTRALIA SUMMARY

Excerpt from a single page statement issued with the full decision today

"The High Court held that a "casual employee" is an employee who has no firm advance commitment from the employer as to the duration of the employee's employment or the days (or hours) the employee will work, and provides no reciprocal commitment to the employer.

"Where parties commit the terms of their employment relationship to a written contract and thereafter adhere to those terms, the requisite firm advance commitment must be found in the binding contractual obligations of the parties; a mere expectation of continuing employment on a regular and systematic basis is not sufficient for the purposes of the Act.

Mr Rossato's employment was expressly on an "assignment-by-assignment basis".

"Mr Rossato was entitled to accept or reject any offer of an assignment, and at the completion of each assignment WorkPac was under no obligation to offer further assignments.

That Mr Rossato was to work in accordance with an established shift structure fixed long in advance by rosters did not establish a commitment to an ongoing employment relationship beyond the completion of each assignment.

"In carrying out each assignment, Mr Rossato worked as a casual employee for the purposes of the Act and the enterprise agreement."

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