Qantas is being squeezed by the rising cost of fuel
Six Qantas flights have been cancelled and 18 cancellations are expected on Tuesday as engineers begin a series of strikes over pay.
The Australian Licensed Aircraft Engineers Association (ALAEA) last week announced action in five major cities after failing to agree a pay deal.
The ALAEA had demanded a 5% wage rise for 1,500 engineers, but the airline has offered 3%.
The wage demands come as Qantas is being squeezed by high fuel costs.
The strikes currently affect only domestic Australian flights.
Qantas executive general manager for people Kevin Brown said that the airline had a "range of contingencies" to deal with the disruptions and that affected passengers would be placed on other flights.
The dispute is expected to continue as union leaders argue that Qantas chiefs have shown no flexibility in meeting their demands.
Qantas, like many airlines, is struggling to deal with a consumer downturn and surging fuel prices.
The firm has already announced a pay freeze for senior bosses and cancelled flights on key routes.
Last month, a two-day strike grounded 17 Qantas flights.