Thousands of Qantas domestic passengers across Australia are facing delays due to a strike by more than 4000 of the airline's ground staff over pay and conditions.
At this stage, 28 flights have been cancelled and 27 flights delayed, on average by 15 minutes, Qantas says on its website.
More than 6000 passengers are expected to be affected.
The Transport Workers Union (TWU) says thousands of staff who turned up to work before the strikes started at 7am (AEST) on Tuesday were turned away.
"They have locked us out since 3.30am," TWU spokesman Mick Pieri told AAP.
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"When we talk about passengers and how they were inconvenienced, everyone has to remember that from 3.30am until 7am Qantas has been on strike not the workers."
Qantas spokesman Luke Enright denied it was a lock-out and said the workers would be paid.
"(Workers that) had come to work and advised they would be striking ... (were told) we can't cause more disruption to passengers by having you come on and off shift," Mr Enright told AAP.
"We will pay you the hours but you won't be required to work."
The four-hour stoppage comes after last-minute talks between the union and Qantas at Fair Work Australia failed to reach a resolution on Monday.
Mr Pieri said the workers were calling for more job security.
"They make it sound like we are asking for the world. We are asking for job protection and the right to go to an independent umpire ... we are still working under a Work Choices document and that's why we are having the problems," he said.
Qantas spokesman Luke Enright said flights were still delayed by up to 35 minutes at Sydney airport at about 7.30am (AEST).
But flights were expected to return to normal by lunchtime.
"Things are going better than expected," Mr Enright told AAP.
"About 90 per cent of our flights (under the new schedule) are departing on time, which is great."
About 150 flights have been affected due to the strike action across Australia, Mr Enright said.
According to the Qantas web page, 11 flights from Sydney have been cancelled, 10 from Melbourne, four from Brisbane, two from Canberra and one from Adelaide.
Olivia Wirth, Qantas group executive of government and corporate affairs, said progress could only be made if the union returned to the negotiating table and stopped the strike action.
"What it does take is for this sort of action to stop," she told the Seven Network.
"If they are serious about these discussions and representing their members they need to continue their negotiations."
Ms Wirth defended the airline's track record as a good employer, saying they paid their baggage handlers 12 per cent more than Virgin staff.
