Proposals for accommodation huts within Kangaroo Island's Flinders Chase National Park will just degrade the wilderness and are designed for the "mega rich", former Greens leader and senator Bob Brown says.
Dr Brown joined a rally of several hundred people on the Parliament House steps in Adelaide on Thursday calling for the development's approvals to be overturned.
"Don't invade this priceless Flinders Chase National Park to line your pockets," he told the gathering.
"There's an 100-year-old national park belonging to all the people being invaded by private enterprise for profit."
Conservation SA and others are concerned over plans by an eco-tourism walking company to establish accommodation units within the national park.
The $4 million proposal by the Australian Walking Company includes two lodges and individual two-person sleeping pods with the company describing the development as environmentally sustainable and having minimal impact.
But Dr Brown said the if the company wanted to build accommodation facilities it should do so on private land.
"I have no trouble with luxurious resorts, but buy your land, do it on the open market and build there," he said.
"The national parks belong to the people and are not a domain for very, very wealthy people to make profit at the expense of the public."
Mr Brown said if there was to be infrastructure in national parks, it should be financed and built by the government and available to everyone.
"Not just the mega-rich," he said.