A wharfies strike around Australia is expected to cost the maritime industry millions of dollars.
An estimated 2000 Maritime Union of Australia members have walked off the job in Fremantle, Sydney, Melbourne and Brisbane as they fight for a range of conditions in a new workplace agreement.
The union said it sought a deal with ports operator DP World Australia that would protect members from outsourcing, casualisation, income protection insurance cuts and automation plans, which could cause job losses.
MUA West Coast deputy secretary Adrian Evans said a sticking point was the company's refusal to include domestic violence leave in the agreement.
"Wharfies have not taken this action lightly, but the insistence of Dubai Ports management on an agreement that would have significant and unacceptable detrimental impacts on workers has left them with no choice," he said on Thursday.
"Dubai Ports claim to be a White Ribbon workplace, but when it comes to supporting employees who become victims of domestic violence, they go missing in action."
But DP World Australia said the union made no material concessions during three months of negotiations and needed to acknowledge the commercial reality of increased competition from automated competitors.
"The union must now make appropriate concessions to their extensive list of claims," chief operating office Andrew Adam said.
He said the action would cause significant disruption to customers and the broader supply chain.
The company's revenue is expected to take a hit of about $1 million, while the industry impact would be more than $1 million.
Lost earnings for employees could total more than $500,000.
The six days of rolling stoppages, which began on Monday, range from 48 to 96 hours in length.
It comes on top of a range of other industrial measures including bans on overtime and shift extensions.
West Australian Premier Mark McGowan urged the company and union to "get together to resolve the issue as soon as possible".