A former state Liberal minister has recounted the struggles of an Indigenous World War I digger as he throws his support behind the Voice to parliament.

James Griffin on Wednesday added his name to a growing list of Liberal MPs distancing themselves from federal leader Peter Dutton's advocacy for the 'no' campaign.

"It is one thing to recognise 65,000 years of Aboriginal connection to this vast land; it is another thing to create a Voice that will help Aboriginal people thrive. It is time to do both," the former NSW environment and heritage minister said in a social media post.

The Manly MP said critics were wrong to conclude the Voice would be ineffective because it was symbolic, saying symbolism could create important practical change such as that occurring at the Aboriginal archaeology site Billagoe since its heritage listing.

"One message I took loud a clear from every Aboriginal community I met with was the value of recognition and listening - to inform practical policy development - and this is what the Voice is about," he said.

He also pointed to the World War I service of Private Albert Knight, a Barkandji man from northwest NSW who was awarded the Distinguished Conduct Medal after leading an attack in France in 1918.

Private Knight enlisted despite not being recognised as a citizen but was among dozens of Aboriginal veterans who won decorations for gallantry in the field, including four Distinguished Conduct Medals and 26 Military Medals, Mr Griffin said.

"The next chapter of Australia should be written with courage, optimism and respect. It can be written with the same courage possessed by Private Albert Knight on the Somme battlefield in May 1918," he said.

Mr Griffin's comments come weeks after federal Liberals resolved to support constitutional recognition for Indigenous people but not a Voice to parliament and executive government.

Mr Dutton says the proposed Voice will be a "new arm of the government" requiring thousands of new public servants and costing billions to run, without improving outcomes for Indigenous Australians

The federal decision bound his frontbench to the 'no' case, leading Berowra MP Julian Leeser to quit his shadow cabinet position.

Dominic Perrottet signed a statement of intent to support the Voice when he was NSW premier.

His successor as state Liberal leader, Mark Speakman, has reserved his position until he has chosen and spoken with his shadow cabinet.

Victoria's Liberal-National opposition is still deciding its position on the Voice, while WA Nationals Leader Shane Love supports a 'yes' vote, as does the country's only Liberal premier, Tasmania's Jeremy Rockliff.