SYDNEY - Workers at Australian state-owned submarine builder ASC began on May 6 a campaign of strikes for higher wages that could disrupt maintenance for Australia's submarines even as it prepares to build the nuclear-powered Aukus fleet.

Roughly 300 workers at ASC's Osborne shipyard in South Australia walked off the job for an hour on May 6, and a separate meeting of union members voted to continue some form of strikes indefinitely, a union official told Reuters.

Osborne is where ASC and British firm BAE Systems will jointly build Australia's fleet of nuclear-powered submarines, the core component of the 2021 Aukus pact between Britain, the US and Australia.

Until that work begins later this decade, the shipyard is where lengthy maintenance is performed on the existing diesel-electric powered Collins-class fleet.

Workers want ASC to match wages across its sites.

Those at Osborne earn about 17 per cent less than colleagues in Western Australia, and the company has only offered a 6.75 per cent raise, according to Mr Stuart Gordon, an assistant secretary for the Australian Manufacturing Workers’ Union.

"The navy doesn't pay its sailors less money if they work in South Australia, so why should it be that way for those who build the ships," he said.

Lengthy industrial action could delay maintenance work on the Collins boats due to begin imminently.

The submarine HMAS Rankin is set to arrive at Osborne in May to begin two years of maintenance work, while HMAS Sheean is at the shipyard and almost finished with a similar cycle of repairs, Mr Gordon said.

ASC said in a statement that unions had rejected multiple offers over six months of negotiations.

Unions also rejected inviting the industrial arbiter, the Fair Work Commission, to decide on the issue, the statement added.

"We will continue to negotiate with the Unions and our workers in good faith, to achieve a mutually beneficial outcome," ASC chief executive Stuart Whiley said in a statement.

A spokesperson declined to give Reuters details of the ASC pay offer.

The Department of Defence was working with ASC to mitigate the impact on submarine maintenance, which should be manageable in the short term, a centre-left Labor government spokesperson said in a statement. REUTERS