Wharfies at DP World's container ports in Sydney, Melbourne and Brisbane have gone on strike this week as disputes continue over a new pay deal.
It is the first time since December 2012 that operations at DP World's container ports on the east coast will be disrupted by industrial action.
The Maritime Union of Australia has received clearance from Fair Work Australia for protected action, stopping work for several hours in Sydney on Wednesday, in Melbourne on Thursday, and in Brisbane on Friday.
DP World has been negotiating with the union since January on a new enterprise bargaining agreement.
The union has rejected the company's offers for east coast workers, which have included wage increases in line with inflation and changes to existing conditions, including new rostering systems and the removal of "picnic days".
The union, which has been pushing for 4 per cent annual wage increases, argues the proposed changes will mean more uncertainty for workers, and that DP World has not catered for the introduction of automation at its container terminals in its proposed agreements.
DP World defended its proposals to MUA workers in September, arguing the union's claims stretched to more than 40 items and were "unaffordable".
DP World offered 3 per cent annual pay rises for four years, and an additional 1.5 per cent for delivering productivity and efficiency improvements.
The company told workers in July that greater competition, as new entrants like Hong Kong's Hutchison Port Holdings started running container terminals in Australia, was creating extra capacity.
"As a result, conditions will remain tough for some time, meaning it is increasingly difficult to maintain the revenue rates we have historically experienced.
"Analysts who follow our industry are predicting weaker growth rates in the foreseeable future resulting in volume growth that is likely to remain relatively flat."
DP World said it "strongly disagreed" with the industrial action and that it was "neither required nor deserved".
"We urge the MUA to withdraw their threat of protected action and return to the negotiating table."
The strikes come as new DP World chief executive Paul Scurrah tries to improve productivity at the group's ports.
Mr Scurrah revealed at a conference in September that only 63 per cent of DP World's existing yard capacity was being used. He also said that only 47 per cent of its existing quay capacity was being used.
DP World Australia claims it controlled 50.4 per cent of the local container ports market in the first six months of 2014.
It backed down from a threat to lock out more than 200 employees at its Fremantle container port in July after striking a deal to continue with talks on its Western Australian agreement.
