ASC is close to completing the third and final ship and says that means it may need to cut 56 production jobs and seven salaried positions.

It will consult with its workforce over the next six weeks and is offering voluntary redundancy packages.

"ASC Shipbuilding takes this action reluctantly and only following a rigorous process of identifying and filling redeployment opportunities to other areas in the ASC Group," the company said in a statement on Tuesday.

ASC said no workers would leave the business immediately and the number leaving could be reduced if further redeployment opportunities were identified in the coming weeks.

The company said it might also be possible for some workers to return once work on the Hunter Class frigates begins in 2020.

Those ships will be built in Adelaide by ASC which is expected to operate by then as a subsidiary of BAE Systems.

The Australian Manufacturing Workers' Union said the further loss of jobs from ASC was evidence the federal government had failed to secure the workforce for Australia's future defence shipbuilding programs.

"Unless there is a trained and skilled workforce in place, the future building programs for frigates and submarines will be badly impacted," AMWU assistant national secretary Glenn Thompson said.

"We are losing those skilled workers who have recently completed the air warfare destroyer program and unless this latest round of redundancies are overturned, they will be lost to the industry, and possibly even leave SA to find new jobs elsewhere."

Federal opposition defence spokesman Richard Marles said Tuesday's announcement represented the third round of job cuts at ASC over the past 12 months, taking total job losses to 372.

Mr Marles said the latest cuts also went against federal government promises that it had stabilised the shipbuilding workforce in Adelaide.

"Every jobs promise the Liberals make results in workers losing their jobs," he said.

South Australian Premier Steven Marshall told state parliament on Tuesday that the federal government understood the importance of defence shipbuilding to SA.

He blamed the previous federal Labor government for creating a "hiatus" between the end of the air warfare destroyer contract and future plans to build offshore patrols boats, frigates and submarines in Adelaide.

"We are working extraordinarily hard on the issue of preparing the workforce here in South Australia and managing that transition," he said.

"The work didn't dry up in the last two weeks."

Australian Associated Press