Australian mining giants BHP and Rio Tinto have joined the push for an Indigenous voice to federal parliament.

The companies released a joint statement on Thursday supporting the 2017 Uluru Statement From the Heart.

The statement calls for a constitutionally enshrined advisory body and a commission to oversee treaty-making and truth-telling.

The BHP chief executive, Andrew Mackenzie, told a business event in Perth his company cannot stand on the sidelines of the issue.

He said BHP would contribute about $1m to a project raising awareness among Australians about the Indigenous voice to parliament, the Cape York Partnership’s Uluru Education Project.

“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,” Mackenzie said.

“That is why we cannot stand on the sidelines.”

The commitment comes after Mackenzie spent the past two months meeting with traditional owners and Indigenous leaders.

“Indigenous Australians have a lot to say to non-Indigenous Australia and non-Indigenous Australia has a lot to learn from them,” he said.

“But the voices of Indigenous Australians are often not heard.

“The Uluru Statement from the Heart is a challenge to hear the unheard.”

Rio Tinto’s managing director, Joanne Farrell, said her company would work with Indigenous communities, state and federal governments and all Australians to help make the Uluru Statement a reality.

“National conversations around constitutional reform must continue as a priority for our country,” she said.

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

The 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 would 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 born out of politics but one that is born 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 view.

He said the government would soon 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.

The Greens leader, Richard Di Natale, said the intervention by the major companies showed how out of touch the coalition was.