The industrial action by the engine components maintenance engineers in Melbourne will begin at 9am on Wednesday.
Heavy maintenance engineers in Brisbane downed tools at 1.30am.
Both groups, totalling about 300 engineers, are planning rallies outside the international terminal at Melbourne's Tullamarine Airport and Brisbane International Terminal later this morning.
The engineers' current enterprise agreement expired at the end of June.
Last month, Qantas engineers went on strike for two hours at major hubs, including Brisbane airport. (Darren England/AAP PHOTOS)
The Qantas Engineers' Alliance - made up of three unions - wants a pay rise of five per cent per year, with a 15 per cent first-year increase to compensate for 3.5 years of "wage freezes and as an industry catch-up payment".
The alliance said Qantas management had refused to return to the bargaining table and increase its previous offer.
"Union members are voting overwhelmingly to escalate our industrial activities," Australian Workers' Union national secretary Steve Murphy said in a statement.
"This is because every time there is a problem at Qantas, the executives ignore it and just hope that it will go away - well, we're not going anywhere."
Comment is being sought from Qantas, which has previously said the engineers' demands are unsustainable.
Last month, more than 1000 Qantas engineers went on strike for two hours at major airports around Australia.
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