The decision on the life-of-type-extension will be made in June, chief executive of government shipbuilder ASC Stuart Whiley said on Wednesday.

But Finance Minister Simon Birmingham did not commit to a date for a decision on full-cycle docking for the submarines.

"We'll let you know what the decision is when we make the announcement," Senator Birmingham said.

The opposition and crossbench are urging the government to make the two decisions together, but Mr Whiley said the ruling on an upgrade would not impact on whether to shift docking to Western Australia from its current site in South Australia.

SA senator Penny Wong accused the minister of holding off for a federal election.

"What are you waiting for? There is no capability reason, there is no sensible reason for delaying for two years," she said.

Governments and industry will need to make capital investment decisions and facility upgrades if docking moves west, along with workers.

Former defence minister Linda Reynolds had promised to make a decision on full-cycle docking last December, as WA lobbies to be host and SA pushes back.

A federal ruling on the docking had already been delayed from 2019, while the upgrade for the Collins is inevitable.

The new Attack Class submarines aren't expected to be delivered until 2035, which means the current Collins Class submarines must be kept in service for much longer than planned.

"There's significant work in the local industry, no one needs to be worried about their jobs," Adelaide-based Mr Whiley said.

"They continue to deliver everything that is asked of them."

Already on the radar of the national auditor, the troubled $80 billion future submarines project is the largest Defence procurement in Australia's history.

Australian Associated Press