Anthony Albanese has been asked to explain whether the Commonwealth will negotiate a treaty with Indigenous people should the Voice to parliament referendum succeed.
The prime minister on Wednesday ruled out the federal government starting the treaty process in this term of parliament, if the vote is passed.
He has been accused by the opposition of dodging questions about the possibility of a federal treaty.
During his victory speech after winning last year's federal election, Mr Albanese committed to implementing the Uluru Statement from the Heart in full.
The statement includes enshrining an advisory body that would be called the "Voice" in the constitution, and a Makarrata commission for the process of "agreement-making" between governments and Indigenous people and truth-telling.
Deputy Liberal Leader Sussan Ley said the government needed to explain what a Makarrata commission was, and why $5.8 million had been set aside for it in the budget.
"Unless Australians get the explanation they deserve, they can't actually sign on to this," she told ABC Radio on Thursday.
"The prime minister comes back to those things, but he doesn't actually explain what he means by treaty, truth-telling, Makarrata."
Victoria and Queensland have already begun their own treaty negotiations with Indigenous communities.
Ms Ley said Mr Albanese was dodging questions by deflecting the issue of treaty to the states.
The Voice is a proposed advisory body that would make recommendations to the federal government and parliament on laws and policies affecting Indigenous people.
The coalition is opposed to the Voice, but supports constitutional recognition of Indigenous people, as well as legislated - but not constitutionally enshrined - local and regional advisory bodies.
The Business Council of Australia on Thursday announced it will back the Voice, and also released data showing its member companies spent more than $1 billion on Indigenous-owned businesses each year.
The council - whose members include BHP, the Commonwealth Bank, Qantas and Woodside - joins a string of community, religious and sporting organisations lending support.
Indigenous Australians Assistant Minister Malarndirri McCarthy said opponents of the Voice were trying to distract from its key purpose.
"It's actually about First Nations people across the country who actually don't have a Voice and would like to be able to influence policy that impacts their lives," she told Nine's Today on Thursday.
"We have to stay focused on that."
A vote proposing constitutional recognition of Indigenous people and enshrining a Voice will be held between October and December this year.