More strike action is expected to hit the beleaguered airline on Monday, with Qantas line engineers announcing they will conduct four-hour work stoppages in Sydney from 3pm (AEDT), Melbourne from 5pm (AEDT) and Brisbane from 4pm (AEST).
Line maintenance engineers conduct the day-to-day checks on aircraft on the tarmac.
Their industrial action is part of an ongoing dispute with the airline over conditions, pay and job security.
A spokeswoman for the Australian Licensed Aircraft Engineers Association (ALAEA) told AAP the union had lengthened the strike action from the usual one-hour stoppages because negotiations with the airline were "still stalling".
"We have had heavy maintenance engineers stop work for a full day on September 30 and October 3, but this is the first time line maintenance engineers have done so," she said.
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Qantas said the stoppages would mean 40 domestic flights would have to be cancelled on Monday and 27 delayed or brought forward.
Eleven international services would also be delayed.
"We will deploy larger aircraft and roster qualified management engineers to operational roles to minimise the impact, however there will still be significant impacts on our passengers," Qantas spokeswoman Olivia Wirth said in a statement on Friday.
If the ALAEA went ahead with the stoppages on Monday, Qantas said, it would take the total number of passengers affected by union strike action to 46,500.
Meanwhile, the union representing customs workers has warned that a series of national stoppages will go ahead next week unless a satisfactory pay deal is reached with management early in the week.
A spokeswoman from Customs and Border Protection told AAP that in the event of a strike a contingency plan had been put in place to minimise disruptions.
