Solicitor-general says voice will 'enhance' government

Australia's second law officer has backed the government's wording for the Indigenous voice, advising it isn't just compatible compatible but "enhances the system".

Attorney-General Mark Dreyfus released the Solicitor-General Stephen Donaghue's 24-page opinion on Friday, amid calls from the opposition to do so.

"The proposed amendment is not only compatible with the system of representative and responsible government established under the constitution, but it enhances that system," Mr Donaghue wrote.

Mr Donaghue dismissed concerns the voice would act as a "third chamber," supporting the primacy of parliament.

"The voice would not form part of either the parliament or the executive government, instead operating only as an advisory body to those two branches of government," he said.

"The voice clearly has no power of veto."

Prime Minister Anthony Albanese said the advice was "very clear and unequivocal". 

"This puts to bed the absolute nonsense of Peter Dutton and Barnaby Joyce ...that they've carried on with, saying that somehow recognising Aboriginal and Torres Strait Islander people in our constitution will lead to Anzac Day being abolished, it is complete nonsense," he told reporters on Friday.

"They are just determined to play politics with this."

Mr Donaghue rejected concerns that empowering the voice to make representations to the executive government would "clog up the courts".

"(It) ignores the reality that litigation concerning the validity of decisions of the executive government is already very common, and that it does not have either of those consequences."

The voice's function of making representations will not "fetter or impede the exercise of existing powers of the executive government", he said.

Nationals MP Keith Pitt said the advice would not influence his opinion that all Australians should be treated equally and the referendum should be voted down.

He said there was still a risk of decisions being taken to court.

"I've seen other (legal) advice which is different. This is always the case until it is tested," he told Sky News.

The solicitor-general's comments were released as a submission to an inquiry into the voice referendum legislation.

The government plans to put the voice to a referendum later this year, between October and December.

Meanwhile, fewer than half of Australians back an Indigenous voice, new polling has revealed.

According to a Roy Morgan survey, support has fallen to 46 per cent of Australians since December.

Mr Albanese said despite the polling result, he remained confident the referendum would pass.

The "no" vote had risen to 39 per cent, up by nine points, while the rate of undecided people dropped two points to 15 per cent.

Victoria is the only state in the country with a majority backing the proposal, with 52 per cent of voters in favour.

Roy Morgan chief executive Michele Levine said the 'yes' vote had lost support over the past months.

"The striking change since December is the politicisation of the issue," she said.