Around 10,000 people are expected to march in Sydney on Saturday to express solidarity with US protestors and demand an end to frequent Aboriginal deaths in custody in Australia.
On the eve of the protest, the police -- backed by prominent local conservatives -- launched legal action to ban the rally on health grounds.
Australia has detected a sustained drop in the number of COVID-19 cases, but social distancing rules remain in force and mass gatherings are not permitted.
The New South Wales Supreme Court was asked to declare the protest illegal.
"We have commenced legal action on the basis that we don't believe the protest can be conducted in a safe way," NSW Police Commissioner Mick Fuller said.
Civil rights protests shaking the United States have resonated with many in Australia -- a country that also wrestles with the legacy of a racist past.
Several protests have already taken place across Australia and the planned march in Sydney is one among several due to take place on Saturday.
Organisers hope to highlight the high levels of imprisonment for First Nations Australians and the large number of indigenous deaths in custody -- more than 400 in the last three decades.
The legal action was a U-turn for the police -- who initially granted the Sydney event the green light -- and follows heavy criticism of the protest in the country's conservative media.
Organisers were determined to go ahead, using a groundswell of public opinion to press for long-stalled reforms.
"Tomorrow, we are going to march if they like it or not, because this is our land and nothing is going to stop any of us," said Latona Dungay, whose son David died in prison in 2015.
Green party parliamentarian David Shoebridge attacked the move as heavyhanded, calling for police to take a more nuanced approach.
"This is not what's needed. This needs cooperation and understanding, not force," Shoebridge said.
Protesters in Melbourne were similarly warned they could face fines for attending a rally in the city, with authorities urging people to stay home.
Earlier on Friday, hundreds of protesters gathered in the nation's capital Canberra even as Prime Minister Scott Morrison urged people to stay home.
"Let's find a better way and another way to express these sentiments rather than putting your own health at risk," Morrison said.
He admitted there was more to be done to address indigenous inequality but continued to reject parallels with the United States.
"Australia is not other places, so let's deal with this as Australians and not appropriate what's happening in other countries to our country at this time."