A planned four-hour strike this afternoon by Qantas union workers has now been called off.
Steve Purvinas, federal secretary of the Australian Licenced Aircraft Engineers Association (ALAEA), said in a statement: "The airline is playing dirty pool with our members by threatening them for taking lawful industrial action."
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A Qantas spokeswoman said the airline had not received official confirmation of the strike cancellation from the union and the planned changes to its schedules would go ahead.
The union says the airline threatened to withhold up to seven hours' pay for the four hours not worked.
"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."
He said the union was now seeking legal advice.
The engineers had planned to walk off the job in Sydney from 3pm.
A Qantas spokeswoman said the airline had cancelled 40 flights and was expecting to delay up to 27 as a result of the strike by engineers. The airline estimated that 46,500 passengers across Australia would be affected by the strike.
Today's events come after 17 Qantas flights were cancelled and another 29 were delayed last Friday despite the Transport Workers Union cancelling its planned industrial action.
Qantas chief executive Alan Joyce said last week he received death threats, a claim dismissed by some unionists as a publicity stunt.
NSW Police are investigating the alleged threats.
The airline has also stepped up its PR offensive, taking out full-page advertisements in most major newspapers apologising for the inconvenience to passengers, and laying the blame for the disruption squarely at the feet of the unions.
More delays at Australia's international airports are likely on Thursday when customs inspectors stop work over a pay negotiation.
The Community and Public Sector Union has rejected the federal government's offer of a 9 per cent pay rise over three years.
Professor Mark Bray, an industrial relations expert at the University of Newcastle, said the number of disputes affecting the national carrier suggested a "campaign by Qantas to reduce costs and confront the unions in a fairly aggressive way at the same time that they are making substantial profits".
"I think it says a whole lot more about Qantas than the unions."
He said the publicity surrounding the disputes - partly because they affected the public - gave the wrong impression that strikes were becoming more common.
"Disputes like this occur in a system of enterprise bargaining. And you can't have this sort of system without the potential for these disputes to occur every two or three years when the agreements are being renegotiated.
"The data suggests that it's just not happening ... that there's an increase in strikes overall in the system."
AAP, Glenda Kwek and Alicia Wood