A group led by Warren Mundine, a former Labor Party national president who is Indigenous, and a group backed by shadow Indigenous Minister Jacinta Nampijinpa Price, will pool their resources for a joint "No" campaign to be called "Australians for Unity".

"It makes sense to merge as it makes our message sharper and more crisp," Mundine told Reuters in a telephone interview.

"It also gives us a great chance to raise more funds and to focus our funds in right direction," he added.

Australians will be asked to vote, likely between October and December, if they want to change the constitution to include a "Voice to Parliament", a committee that can advise lawmakers on matters that affect the lives of Indigenous people.

Making up about 3.2% of Australia's 26 million population, Aboriginal people were marginalised by British colonial rulers and are not mentioned in the 122-year-old constitution.

While a majority of Indigenous people support the Voice, others, like Mundine and Price, argue it is a distraction from achieving practical and positive outcomes, and that it would not fully resolve the issues affecting them.

Mundine said setting up an Indigenous body in parliament will only add another layer of bureaucracy.

"It's not going to fix some of the issues affecting the community. We need to deal with the underlying issues," he said.

A YouGov poll out last month showed 83% of Indigenous Australians would vote for the constitutional change. A wider poll by the Guardian newspaper found that 60% of Australians would support it.

Any constitutional amendment requires a national referendum.

To succeed, a referendum requires a majority of votes nationally, as well as a majority of votes in at least four of the six states.

Prime Minister Anthony Albanese has staked much of his political capital on the referendum in a country that has only passed eight out of 44 since it became independent.

The most recent one was in 1977.

The conservative Liberal-National opposition coalition will oppose the national vote.