Former prime minister Scott Morrison has used a rare speech in parliament to oppose the upcoming Indigenous voice referendum.
Mr Morrison said the proposal was "ill-defined" and would create constitutional risk in enshrining an Indigenous voice to parliament and executive government.
"It is not necessary to enshrine the voice in the constitution to deliver constitutional recognition for Indigenous Australians," he told parliament on Wednesday.
"That enjoys broad support.
"It is wrong to conflate the issues of the voice with constitutional recognition and treat them as inseparable.
"The impact of the voice on the operations of executive government and the parliament are also not known, presenting significant and unknown risks that cannot be easily remedied."
It was just the third time Mr Morrison has spoken in parliament since losing last year's federal election - the other occasions being after the death of the Queen and to defend himself from being censured following his multiple ministries scandal.
The former leader said the voice would create unnecessary risks to the operation of government and the executive, and would not succeed in closing the gap between Indigenous and non-Indigenous people.
"Permanently changing the constitution in the way the government proposes will sadly not change the desperate circumstances being experienced in so many Indigenous communities across Australia," he said.
"I understand that that is the hope of the proposal, and hope is a good thing, but hope disappointed will be crushing to the soul.
"And such disappointment can be reasonably foreseen by proceeding with the government's proposal."
Mr Morrison took aim at sporting codes and business groups that have publicly supported the referendum.
"While keenly interested in the NRL's opinion on hip-drop tackles and the six-again rule, I don't think I'll be referring to them for constitutional advice in making my decisions on this matter," he said.
While he was prime minister, Mr Morrison rejected calls to establish a voice to parliament in the constitution but backed work to set up local and regional voice mechanisms.
A proposal to have the body legislated did not proceed.
Indigenous Labor MP Marion Scrymgour said the voice was an extension of advocacy from Aboriginal leaders, not a political campaign.
"This constitution, this birth certificate which we now seek to amend in such a modest way was predicated on allowing the participating colonies to complete the project of cancelling out Aboriginal people, which they had already embarked upon," she said.
"Giving our people a real voice now is the least that this country can do to make good the wrong that has existed at the heart of our founding document."
Ms Scrymgour decried opponents of the voice who said the constitutional change would divide the country by race.
"It is disgraceful that people use that as a means to create doubt and division in the hearts and minds of people," she said.
Labor frontbencher Anne Aly said the cost of the referendum failing would be too high.
"We have a choice, whether to write a future for this country where all people walk together and where we no longer have Aboriginal and Torres Strait Islander people (with) higher mortality rates, higher incarceration rates, lower education rates, lower school completion rates," she said.
"The other choice is that we relegate the voice of our First Nations people to the margins of history."
MPs face another long night of talks on the voice, ahead of a vote next month on the final form the referendum will take.
The lower house isn't expected to vote on the voice bill until next week when the debate will shift to the Senate.
The bill is expected to be finalised in June ahead of the referendum, which will be held between October and December.
