The Federal Court in May 2020 found casual workers employed on a regular, permanent basis were entitled to annual, sick and other leave entitlements.

The decision found Robert Rossato was entitled to be paid by his former employer a 25 per cent casual loading along with leave entitlements because of his regular pattern of work, backing up an earlier court ruling.

But the High Court on Wednesday unanimously allowed an appeal from labour hire company Workpac, which had employed Mr Rossato.

The High Court held that a casual employee has no firm advance commitment from an employer about the duration of their employment, their days or hours of work, and the employee provides no reciprocal commitment to the employer.

Rossato’s employment was expressly on an “assignment-by-assignment basis”, the court said.

He was entitled to accept or reject any assignment and the fact he was rostered long in advance did not establish a commitment to an ongoing employment relationship.

Australian Mines and Metals Association chief executive Steve Knott last year said the case would be one of the most important employment law issues the High Court had 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.

But the mining union argued the Federal Court had twice confirmed the “permanent casual rort” in the industry is unfair and unlawful.

“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,” CFMEU mining and energy general president Tony Maher said.