About 200 Maritime Union of Australia supporters have marched on the Brisbane offices of Rio Tinto, after the crews of two bulk carriers were sacked and replaced by cheap foreign workers.

Pacific Aluminium, operator of the Tomago aluminium smelter in NSW’s Hunter Valley, is wholly owned by Rio Tinto.

In January this year, the company notified the crew of the CSL Melbourne – who had carried alumina from Gladstone to the Tomago smelter for five years – that they were no longer needed.

Before the announcement, Pacific Aluminium reportedly secured a licence from the Federal Government that enabled it to transport the alumina aboard an overseas-flagged ship.

This ship could be crewed by workers with no legal entitlement to Australian wage rates.

The replacement of CSL Melbourne’s crew of follows almost identical moves against the crew of the MV Portland last year.

The Portland also carried alumina, running a route from Western Australia to Alcoa’s Victorian smelter for 28 years.

“The demonstration today is about workers on the MV Portland and CSL Melbourne being removed from their place of work, and it’s about job security for the future for our children”, the MUA delegate on the Portland, Dale Eaton, told reporters.

“We’re under attack at the moment. They’ve already attacked manufacturing, now they’re attacking shipping, and we don’t know where they’re going to next”, he said.

Unions members say there has been a “Thatcherite” response from authorities, including sending dozens of NSW police on board the CSL Melbourne to remove the crew.

The weekend’s protest in Brisbane was one of several held around the country to draw focus to the issue, including significant rallies in Newcastle and Darwin.

The union has joined others in a campaign focused on a “jobs embassy” outside Parliament House in Canberra, which has been used to argue for conditions to be maintained amid broad IR upheaval.