The federal opposition’s Indigenous affairs spokesman says his support for the voice referendum is waning as he seeks more details on the proposal.

It comes as campaigners say younger Australians who “own up” to the dispossession of Indigenous people will be crucial for the referendum to succeed.

The country will vote later this year on enshrining an Indigenous voice in the constitution to advise the government on policies affecting Aboriginal and Torres Strait Islander peoples.

Opposition Indigenous Australians spokesman Julian Leeser, who says he is a long-time supporter of the voice, will use a speech to Young Liberals on Saturday to call for more detail on how the voice will work.

“The way the government is handling this referendum they are losing supporters daily,” he will say.

“They are even in danger of losing me.”

Mr Leeser’s speech doesn’t specify what details on the voice he is seeking.

In November, the Nationals announced they would oppose the voice as a party, while Opposition Leader Peter Dutton has called for more detail on the proposal as the Liberals remain undecided on their support.

The “yes” campaign faces an uphill battle for success as the last referendum to pass was held in 1977.

Cobble Cobble woman Allira Davis, co-chair of the Uluru Youth Dialogue, said supporters of the voice were focused on educating young non-Indigenous Australians about the “yes” campaign.

She said the group was reaching out to young people at universities and sporting events to help spread the word in person and on social media.

“Young people are progressive – even with the climate action movement and marriage equality, a lot of those campaigns are led by young people,” Ms Davis told AAP.

“So we are trying to inform our young Australians about the need to see change in our lifetime.”

Ms Davis said educating younger people and finding allies would help inform older non-Indigenous people – who will make up the majority of voters in the referendum – about the importance of the voice.

Australia has unfinished business with its First Nations people, she said, as one of the only countries without any official recognition of or treaty with them.

Apart from giving Indigenous people a say about their own destiny, a voice to parliament will also have an important role in explaining what has happened and is still happening to Aboriginal and Torres Strait Islander peoples. 

Ms Davis said the often harsh business of truth-telling was something that had been absent from the national conversation, although that was changing among younger generations of non-Indigenous Australians.

“We haven’t been listened to since colonisation, we need to talk about what has happened in our history,” she said.

Ms David added the truth-telling process was not about blaming current generations for acts of the past.

“It’s just having the truth said and told so that we can move forward on this journey towards a better future for Australia,” she said.