Protesters have used white twine and red umbrellas to form a human 'Stop Adani' sign outside Parliament House.
More than 200 activists gathered to speak out against a possible $1 billion public loan for the Indian company's Queensland coal mine.
"If this mine goes ahead it's going to be the biggest mine in our history," said Sarah Ellyard, a protester struggling to keep hold of a number of #StopAdani signs.
"It's an area about five times the size of Sydney Harbour. It's not compatible with a safe climate future."
Labor senator Lisa Singh, a vocal critic of the mine, said government arguments about its economic benefits needed to challenged.
"It's not just how we feel," she said. "It's the science and the economics that is important in this debate."
Australia should be focused on renewables, especially with India reducing its coal imports in the near future.
"Because that is the future of our country and, indeed, the future of our planet," Senator Singh said.
Greens leader Richard Di Natale said he would be taking to task representatives from the North Australia Infrastructure Facility - under whom the $1 billion loan would be provided - when they appear at a Senate inquiry on Friday.
"We're going to be doorknocking in marginal seats right across the country with you, making sure millions of Australians understand why this mine can't go ahead," he said.
"If we can't stop this mine in the parliament we're going to stop it by standing in front of those bulldozers and making sure this mine never gets built."
Wandering around the event wearing a giant Malcolm Turnbull mask was protester Matthew Armstrong.
The reason activists were protesting was because of the power wielded by conservative elements in the government, he said.
"The only way we can counterbalance that power they have is through popular protest," he said in a muffled voice.