As a referendum on the Indigenous Voice to Parliament draws closer, the Greens have raised concerns about thousands of First Nations people who will be unable to have a say on the issue.

Currently, people serving a sentence of more than three years in prison are not eligible to vote in federal elections or referendums.

The latest ABS data shows around 42,000 people are currently in prison around the country and about 13,000 of them are Aboriginal or Torres Strait Islander.

The Greens have put forward a change to the referendum machinery bill – being debated in parliament this week – which will allow incarcerated people to vote in the referendum.

Greens Senator Larissa Waters says people should not be “double punished” by withholding their vote from the referendum.