Union Flag, by Spanish artist Santiago Sierra, will see the British Flag immersed in the blood of the First Nations peoples from territories colonised by the British Empire.

Dark Mofo is inviting people to take part, with participants required to donate a small amount of blood for the artwork - which will be facilitated by a medical professional before the festival.

Expressions of interest are only open to First Nations peoples from countries and territories colonised by the British Empire at some point in their history, and who reside in Australia.

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One participant will be randomly chosen to represent each country, and blood will only be taken from those selected.

The blood taken will be no more than the standard amount for a blood donation.

The flag will be put on display during the 2021 festival once it is immersed in blood.

Sierra said in an open letter that the intent of the project was against colonialism.

"It is an acknowledgement of the pain and destruction colonialism has caused First Nations peoples, devastating entire cultures and civilisations," he said.

"The First Nations people of Australia suffered enormously and brutally from British colonialism.

"Nowhere more so than in Tasmania where the Black War in the early nineteenth century had a devastating impact, almost killing the entire Tasmanian Aboriginal population - an act that has since been defined as genocide."

Tasmanian Aboriginal Centre's campaign manager Nala Mansell said Aboriginals had given their support to the Spanish artist for acknowledging the blood shed during invasion.

However, she said they felt enough blood had already been shed, and they did not want to shed any more.

Ms Mansell called for the Australian flag to also be immersed in blood because "the war against Aborigines didn't end when the shooting stopped".

Dark Mofo's creative director Leigh Carmichael said the announcement of Union Flag was the result of almost two years of work between the artist's studio and the festival team.

"Sierra's work is complex, sometimes confronting and much of his work tends to deal with social inequities," he said.

Mr Carmichael said the work was a logistically difficult project, but the team were working to ensure it would come to fruition.

"This call out to First Nations peoples from countries claimed by the British Empire at some point in history to participate is the first public phase of the project.

"We hope to receive interest from as many people across Australia as possible."

Dark Mofo's full program will be released in early April, and the festival will run from June 16-22 in Hobart.

To register interest in Union Flag visit darkmofo.net.au/blood