Labor and the Greens fear new plans for Rottnest will threaten the island's pristine environment and do nothing to make holidays more affordable.
The new strategy recommends the private sector runs half of the island's accommodation and builds and operates a marina.
It also allows for new ecotourism accommodation on Mary Cove on the island's isolated southern coast, and would be the first time accommodation was allowed within the current boundaries of the A-class conservation reserve.
Greens MP Lynn MacLaren fears the island's natural and heritage values will be "lost in the back pockets of private investors" under the plan.
"Many West Australians do not want to see Rottnest - a unique and treasured place - carved up beyond recognition," she said.
Fremantle Labor MP Simone McGurk said the Barnett Government needed to tread carefully in opening the A-class reserve to accommodation.
"To describe a new tourism venture as ecotourism is one thing, ensuring it does not encroach on what is now a world-class environmental sanctuary is another," she said.
Ms McGurk said some aspects of the plan made sense, including the relocation of industrial or back-of-house activities away from main tourist traffic and improved access to popular areas such as The Basin.
Rottnest Society convenor Eric Moxham said the plan signalled the end of the Rottnest that most West Australians had grown up with and loved.
He said the Government had an obligation to manage and maintain the island.