The High Court granted Mondelez special leave to appeal a Federal Court decision against it in its stoush with the Australian Manufacturing Workers Union.

Under the Federal Court ruling, staff who worked three 12-hour shifts at the Hobart Cadbury factory each week accrued 120 hours of leave each year.

But a worker who did the same 36-hour week across five shifts would only accrue 72 hours of personal leave - including sick and carer's leave - a year.

The appeal was only brought on by the Morrison government, with Attorney-General Christian Porter blaming discrepancies in Labor's wording of the Fair Work Act in 2009.

AMWU chief executive Paul Bastian said the government should be on the side of Australian workers.

"It's appalling to once again see the Morrison Government take the side of a profitable multinational company over some of the hardest working, lowest paid employees in this country," Mr Bastian said.

He said the union was ready for the upcoming fight, saying it was a decision that affected any shift worker.

"If you're working 12-hour shifts and need to take a sick day, then you should be paid for your normal hours of work, it's as simple as that," Mr Bastian said.

The mining sector lobbyists, the Australian Resources and Energy Group (AMMA), welcomed the decision from the High Court.

Chief executive Steve Knott said the original decision would create unequal conditions between employees and significantly cost businesses.

"The inequities it creates would be damaging to workplace culture and harmony," Mr Knott said.

Australian Associated Press