Australia's largest submarine telecommunications cable operators have unanimously backed proposed changes to cable protection laws currently being considered by the Senate.

Southern Cross Cables, Telstra, SingTel Optus, Australia-Japan Cable (AJC) and Basslink said in a joint submission (pdf) to a Senate inquiry that proposed legal changes broadly reflected alterations they had collectively sought since early 2011.

The proposed changes include harmonising Australia's cable protection regime with international rules, protecting domestic subsea routes in addition to international links, and simplifying permit application processes.

They also aim to give security agencies the power to assess new subsea projects and veto any that are deemed counter to Australia's national interests.

A submission by the Attorney-General and Communications departments (pdf) sheds further light on this veto power, noting it would only be enacted in "rare circumstances" where security concerns could not be adequately resolved by the cable operator.

It was considered more likely that the powers would enable "potential security concerns relating to the installation of submarine telecommunications cables to be identified and addressed where possible, in consultation with the applicant, at an early stage prior to the construction of the infrastructure."

The Attorney-General's assessment of cable projects would in turn rely on a security assessment conducted by ASIO.

"A security assessment by ASIO would form the basis of consideration by the Attorney-General whether to exercise his or her power to direct the ACMA to not grant a permit," the departments noted.

"That is, the Attorney-General would only exercise the power where an adverse or qualified security assessment is issued by ASIO."

Operators stung by an adverse ASIO assessment could apply for a merits review of the security agency's decision.

The Government also appeared to rule out blurring the lines of the Senate inquiry to scope the threat posed by security agencies themselves using subsea cable infrastructure to eavesdrop.

Greens Senator Scott Ludlam said late last year he hoped the Senate inquiry would examine the risks posed by malicious tapping of submarine cables, in the wake of revelations that this method was employed by the US National Security Agency (NSA).

However, the Government, through its departments, indicated that "the interception of telecommunications services falls outside the scope of … the Bill."

The submarine cable operators simply noted that they complied "with relevant legislated obligations".

"This includes lawful interception requests from an Australian law enforcement agency," the operators said.