A chocolatier has claimed a sweet victory after a bitter legal row with the union over sick leave entitlements.
The High Court has sided with Mondelez International, which owns Cadbury, over how leave is accrued.
Mondelez has welcomed the decision, saying it will level the playing field between workers on different shifts.
Business groups have also breathed a sigh of relief, given the case could have knock-on impacts for other shift workers.
The stoush centred on whether employees who did 12-hour shifts were entitled to more leave than those whose hours were more spread out.
In a 4-1 decision, the court agreed when an employee is entitled to 10 days of paid personal leave a year, it is considered a "notional day".
This amounts to one-tenth of the equivalent of an employee's ordinary hours of work in a two-week period, rather than a "working day" consisting of time worked in a 24-hour period.
Chief Justice Susan Kiefel, Justice Geoffrey Nettle and Justice Michelle Gordon rejected the latter definition.
"It would give rise to absurd results and inequitable outcomes, and would be contrary to the legislative purposes of fairness and flexibility in the Fair Work Act," they said.
"The 'working day' construction would create not only unfairness but also uncertainty."
Justice James Edelman agreed with the orders put forward by the trio, but used a different approach to reach his conclusion.
Justice Stephen Gageler disagreed, saying 10 days should mean 10 periods of 24 hours.
Employer groups believe the decision will have implications for more than one million people doing shift work, particularly in the mining, manufacturing, construction and nursing sectors.
The Australian Industry Group is elated, saying the decision preserves widespread industry practice.
"The court's judgment ensures equity amongst full-time and part-time employees, and amongst 8-hour and 12-hour shift workers," Ai Group boss Innes Willox said.
The court set aside a landmark ruling from the Federal Court, which found employees 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.
Industrial Relations Minister Christian Porter backed the Mondelez appeal, saying the initial ruling sparked confusion and uncertainty about calculating sick and carers' leave.
Mr Porter blamed Labor's rewording of the Fair Work Act in 2009, when the annual entitlement was changed from 76 hours to 10 days.
The Australian Manufacturing Workers Union criticised the government's involvement in the case.
Australian Associated Press