Former boxing world champion Anthony Mundine has joined the 'No' campaign on an Indigenous Voice to Parliament, saying the proposal would be "detrimental" to First Nations people.

Mr Mundine posted an 18 minute-long video to his Instagram account on May 18, asking Indigenous people, supporting 'Yes', to reconsider their stance on the Voice.

Activist and Widjabul woman of the Bundjalung Nation Mebbingarri Cindy Roberts joined Mundine in the video.

The pair claimed the referendum was an effort to end Indigenous sovereignty, instil a "new world order", and said Indigenous people were being "coerced" into pushing a disingenuous agenda with claims of "bribing", - seemingly in reference to one-off grants of up to $15,000 offered by the Yes23 campaign, reportedly with intention to help Indigenous community groups engage with the campaign.

Mr Mundine said there are attempts to make Indigenous people "British subjects" with their recognition in the constitution.

In a piece broadcast by SkyNews on Monday, Mr Mundine repeated some aspects with reporter Caroline Marcus, who he told the Voice is a "takeover".

"Not just Aboriginal people, but all people will be f-*-*-*-e-d. That's it," Mr Mundine said.

"Once our sovereignty is ceded, then we will have no power.

"Why the hell do we need the Voice? We've got people in Parliament. We got senators. We're already making our voices heard."

Mr Mundine said of organisations and notable Indigenous Voice advocates supporting the referendum, "everyone's getting paid".

Prime Minister Anthony Albanese and constitutional experts have said the Voice to Parliament would not impact First Nations sovereignty.