The opening planned for Feb. 5, was cancelled late on Thursday, with authorities in Western Australia citing health risks from a surge in the Omicron variant of coronavirus in eastern states.
In a statement, Qantas said, "The group retains the flexibility to adjust flying levels depending on demand and clarity on border re-opening in the weeks and months ahead."
Last week, the airline had pared about a third of planned domestic and international capacity in the March quarter, to better match demand amid rising COVID-19 infections.
Preparing for a surge in demand, it had recently recalled about 11,000 staff who had been idled without pay during the pandemic.
The move increased fixed costs and the recent capacity cuts will squeeze revenue and reduce margins.
Qantas, which ends its financial year in June, said it would give more details on the impact of the changes in half-year results late next month.
Rival Virgin Australia said it would review its flight schedule to Western Australia to keep in line with the state's arrangements to re-open its borders.
(Reporting by Jamie Freed; Editing by Clarence Fernandez)