But the prime minister says their views won't change his own.

The companies are expected to make a joint statement on Thursday supporting the 2017 Uluru Statement From The Heart, which called for a constitutionally-enshrined advisory body and a commission to oversee treaty-making and truth-telling.

BHP chief executive Andrew Mackenzie is set to tell a business event in Perth his company cannot stand on the sidelines of the issue during a speech on reconciliation with indigenous Australians.

That's why it will contribute about $1 million to a project raising awareness among Australians about the indigenous voice to parliament, the Cape York Partnership's Uluru Education Project.

"We believe that the constitution should be amended so that the voices of indigenous Australians can be fully heard," Mr Mackenzie is expected to say, according to The Australian.

"The longer I've been at BHP, the more certain I've become that this great company, like this great country, has unfinished business with the indigenous peoples of Australia.

"That is why we cannot stand on the sidelines."

Federal Labor has vowed to initiate a referendum on enshrining an indigenous voice to parliament in the constitution if it wins government.

But Prime Minister Scott Morrison last year emphatically rejected the idea, claiming it would be nothing more than a "third chamber" of power.

On Thursday, he said it will be up to the shareholders of BHP and Rio Tinto to cast judgment on their position.

"They have a perspective on this issue which isn't borne out of politics but one that is borne out of their deep cooperation with indigenous people around the country," he said.

But he said it won't "make any difference one way or another" to the coalition's position.

That comes as the government prepares to respond to a November report from a bipartisan committee, which told it to initiate a co-design process with Aboriginal and Torres Strait Islanders to develop an indigenous voice to parliament,

Greens leader Richard Di Natale said the intervention by the major companies - which he welcomes - shows just how out of touch the coalition is.

"Malcolm Turnbull to his great shame ruled out supporting this very strong statement," Senator Di Natale said.

"You have to give Aboriginal people a strong voice in determining and shaping their own future. These top-down, paternalistic solutions - again, by successive governments - they fail."

Australian Associated Press