Qantas says it has been forced to ground five aircraft because of an industrial dispute with its engineers.
The airline has cancelled almost 400 flights over the next month because of the dispute over pay and job security.
Operations head Alan Milne says work bans by the union have led to a backlog of maintenance work.
He says the planes could be grounded for up to a month, or longer.
But the union for aircraft engineers says the airline is lying. It says Qantas has grounded some of its planes because they are for sale.
On Sunday night a Qantas 747 jumbo bound for Sydney was forced to return to Bangkok after the pilot had to shut down an engine. A passenger reported seeing sparks from one of the engines.
Mr Milne says there were no safety issues.
The ABC reports Qantas management and the engineers will meet Fair Work Australia in Melbourne on Thursday.