Wharfies will continue striking across key Australian ports amid a pay fight with the country's largest stevedoring company.

More than 1800 workers at DP World are striking this week in Sydney, Melbourne, Brisbane and Perth.

It comes after a three-month ceasefire agreement between the company and the Maritime Union of Australia.

The union claims it is fighting the outsourcing of jobs, cuts to income protection insurance and plans for automation which could cause job losses.

"Management initially used the wellbeing of workers and their families as a bargaining tool, and wharfies don't take kindly to that kind of corporate bullying and intimidation," according the the union's assistant national secretary, Warren Smith.

He said the company had stepped up the conflict with workers when it stripped them of income protection insurance.

"We will not roll over and accept an unfair agreement, we won't accept unilateral attacks on workplace rights and conditions, and we won't stand by while outsourcing and automation are used to axe quality jobs from the Australian waterfront," Mr Smith said.

But DP World says the union has refused to make any concessions on their 50 claims.

"These claims include a wage increase well above CPI (the consumer price index), without any willingness to support the needs of (the company)", its chief operating officer Andrew Adam said.

"The union continues to demonstrate an alarming refusal to acknowledge the commercial reality of the intense competition from automated competitors."

Mr Adam said the nationwide strikes would affect shippers, exporters and importers.

Changes to global shipping and an excess number of workers had created challenging financial conditions for the company.

More than 600 wharfies went on strike in Melbourne on Wednesday and they don't plan to return to work until Sunday.

Stranded goods could include consumables and medical supplies.

Victoria's acting premier Lisa Neville called on DP World and the union to sit down and find a solution.

Meanwhile, the state opposition's industrial relations spokesman Nick Wakeling blamed the strikes on government, pointing to close links between Labor and the union.

Another 600 workers in Sydney and about 250 in Fremantle are expected to walk off the job for two days from Thursday.

In Brisbane, more than 300 workers took industrial actions on Monday and Tuesday.