Major employer groups have cheered the High Court's decision to allow special leave to appeal a landmark ruling on leave entitlements for long-term casual workers.
The Federal Court in May found casual workers employed on a regular, permanent basis are entitled to annual, sick and other leave entitlements.
Labour hire company WorkPac was on Thursday granted special leave to appeal the ruling, which found in favour of former employee Robert Rossato.
The decision found Mr Rossato was entitled to his 25 per cent casual loading along with leave entitlements because of his regular pattern of work, backing up an earlier ruling.
Australian Mines and Metals Association chief executive Steve Knott said the case would be one of the most important employment law decisions the High Court has considered.
"Should the Federal Court's decision stand, thousands of employers across all sectors of the economy would face the threat of back pay claims, estimated to be at least $18 billion," he said.
The mining union argues the court twice confirmed the "permanent casual rort" in the industry is unfair and unlawful.
CFMEU mining and energy general president Tony Maher said the appeal would delay long-overdue justice.
"The model embraced enthusiastically by big mining and labour hire companies is to replace good permanent jobs with lower-paid casual jobs and it's a straight-out scam," he said.
"Casual mineworkers do the same work on the same rosters, but they are paid about 30 per cent less and have no job security or leave entitlements."
Mr Maher described employers' concerns about costs to businesses as hysterical.
AMMA and the Australian Chamber of Commerce and Industry want parliament to change the law before the court action is decided.
"Employers and employees need to see common sense and confidence restored much sooner than the High Court appeal process will likely take," ACCI chief executive James Pearson said.
"No Australian expects to get paid twice for the same thing, and no business should be required to pay twice for the same entitlement."
Australian Industry Group chief executive Innes Willox said the rulings had alarmed businesses and stopped them hiring.
"With more than half a million casual jobs lost since March, any barrier to casuals being re-employed is not in the interests of employees or employers," he said.
The appeal is due to be heard next year.
Australian Associated Press