A legal decision that means workers rack up personal leave at different rates despite working the same fortnightly hours could be appealed in the High Court.
Attorney-General Christian Porter says the recent Federal Court decision in Mondelez vs AMWU created significant inequities between employees.
Under the ruling, a Mondelez staff member 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 a year.
"The change to the definition is relevant to every business where shifts are worked," Mr Porter said on Monday.
He blamed Labor's wording of the Fair Work Act in 2009 for the discrepancy, which he believes could cost businesses up to $2 billion a year.
The coalition will seek leave in the High Court to appeal the ruling to ensure all full-time staff who work a 38-hour week were entitled to 76 hours of personal leave a year.
During the court case, the union argued Australia's National Employment Standards mandate a minimum of 10 days paid personal leave per year.
"Cadbury employees work ordinary hours of 12-hour days, which means they should have access to 120 hours of paid personal leave per year to cover the hours of 10 work days," the union said.
Mondelez has announced it intends to lodge its own appeal.
AMWU national secretary Paul Bastian says the attorney-general is "wilfully misrepresenting" the court decision, accusing Mr Porter of siding with big business.
"The Mondelez decision is about ensuring that shift workers who work ordinary hours of more than 7.6 hours a day have the same ten days of sick leave as any other worker," Mr Bastian told AAP in a statement.
"It's about basic fairness."
Australian Chamber of Commerce and Industry chief executive James Pearson said the decision had created confusion.
"Australians have long had access to personal/carers' leave entitlements based on an average of the ordinary hours they work, no matter the shift lengths they work," Mr Pearson said.
"The decision as it currently stands will lead to unreasonable, unintended results, and create friction between employees due to substantial inconsistencies in leave entitlements.
The Australian Industry Group also supports the appeal.
"In addition to the cost impacts, the decision would impose a major barrier to employers agreeing to part-time employment arrangements, including for employees returning from parental leave," chief executive Innes Willox said.
Australian Associated Press