Passengers are not expected to face flight cancellations or delays as Qantas engineers walk off the job for 24 hours over a stalled pay deal.
The industrial action by 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 terminals at Melbourne and Brisbane airports later this morning.
The engineers' current enterprise agreement expired at the end of June.
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 three and a half 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."
Last month, more than 1000 Qantas engineers went on strike for two hours at major airports across Australia.
Qantas does not expect Wednesday's industrial action in Melbourne or Brisbane to have any impact on customers.
"There's been some industrial action by engineers since late September and so far we've been able to successfully ensure it hasn't resulted in any flight delays or cancellations," a Qantas spokeswoman said.
The airline says the engineers' demands are unsustainable.
Qantas said it has had meetings with the unions and wanted to find a way forward but they had chosen to take action.
"Our preference is to reach an agreement that includes pay rises and other benefits," the Qantas spokeswoman said.
"This includes annual pay increases, increased apprentice pay, as well as new career progression opportunities and more advanced training."
