Embattled carrier
Line maintenance engineers, who check aircraft on the tarmac, were planning to stop work for four hours as part of a labour dispute in Sydney, Brisbane and Melbourne.
But just hours before walking off the job the Australian Licenced Aircraft Engineers Association (ALAEA) cancelled the strike, saying Qantas had threatened to withhold up to seven hours' pay for the time not worked.
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"The airline is playing dirty pool with our members by threatening them for taking lawful industrial action," ALAEA Federal Secretary Steve Purvinas said.
"To ensure our members are not unfairly disadvantaged by Qantas management's last-minute curve ball, we have decided to reassess our position on today's planned action.
"We are currently seeking legal advice and if necessary we will launch legal action against the airline for unlawful adverse action against our members," he added in a statement.
It is the second time in less than a week that unions have threatened to strike then called it off at the last minute, creating confusion.
On Friday, a planned stoppage by baggage handlers and ground staff was put on hold, but too late for Qantas to avoid disruptions for 5,700 travellers.
It was a similar story Monday with Qantas saying it had not been given enough notice to revise its flight schedules, with the travel plans of 11,000 passengers affected.
"In a clear sign that this was an intentional game by the union, the media have been notified that the strikes have been cancelled. However Qantas has still not been formally notified," the airline said.
Spokeswoman Olivia Wirth added that the ALAEA was clearly intent on causing severe disruptions.
"We apologise to all of our customers who have been delayed because of cynical games from the union," she said.
"We would like to re-instate services but it's too late. You can't just turn an airline on and off."
She said 40 domestic flights had been cancelled and another 38 services were delayed or brought forward.
Several international flights were affected, with delays of more than two hours on some services to London via Bangkok and Singapore, Frankfurt via Singapore, and to and from Auckland.
Wirth admitted Qantas notified employees they may not be paid if they took industrial action, but denied "baseless claims from the union" that a threatening letter was sent.
Unions are locked in protracted contract talks over pay and conditions with Qantas, which has said it will slash 1,000 jobs as part of its new Asia focus.
On Friday, Australian police said they were investigating alleged death threats against chief executive Alan Joyce, while the airline has said managers had been sent menacing letters and strike-breaking workers bullied.
