The state opposition will look to the Parliament to block proposed changes to the state's marine parks.
Changes include opening the Cape du Couedic Sanctuary Zone off the southwest corner of Kangaroo Island to commercial rock lobster fishing.
SA Labor says Environment Minister David Speirs has "slashed" three marine sanctuaries, despite a scientific review he commissioned providing the opposite advice.
The 577-page document, produced by Adelaide-based consultants BDO Econsearch, found the economic benefit of opening up the zones to fishing was minimal and that: "Modifying the...zoning arrangements...will reduce the effectiveness of the marine park network in protecting and conserving marine biodiversity habitats."
The SA rock lobster industry supports opening up the Cape du Couedic sanctuary zone off Kangaroo Island for its fishing activity, saying using baited pots had minimal impact on the environment.
To preserve conservation efforts sanctuary zones at Nuyts Reef and Isles of St Francis off the west coast would be expanded to see an overall increase in marine environment protected.
Shadow Minister for Environment Susan Close said the state government commissioned the BDO review in 2018, but alleges it kept the results hidden until Minister Speirs overturned its findings.
The government then announced plans to open up marine park sanctuaries to commercial fishing in the Neptune Islands, Cape du Couedic and the Clinton Wetlands in Gulf St Vincent, she said.
"The Minister also misrepresented the views of environment groups with claims they were supportive of the proposals, when they are staunchly against them," she said.
"Thousands of emails from South Australians opposing this destruction of our precious environment have been sent to SA Labor, the premier and the minister," Ms Close said.
"In a week when the United Nations handed down a damning report outlining the horrific loss of biodiversity across the planet, David Speirs responds by secretly cutting marine park sanctuary zones."
The minister responded to Labor's allegations.
"The Marshall Liberal Government is committed to protecting our state's marine environments while also supporting the communities that depend on this resource," Mr Speirs said.
"We know that for many of our regional communities and industries, 2020 has been a very tough year with bushfires and the significant impacts of a global pandemic.
"We know Kangaroo Island in particular has been devastated and the proposed changes would provide a significant boost to that local community.
"Creating jobs in regional communities and supporting livelihoods is a real priority for our state and we believe these changes support those communities doing it tough and provide appropriate protection for our marine environment.
"The proposed changes would allow some fishing in areas where it has previously been banned but also see the expansion of other sanctuary zones to improve conservation outcomes.
"I'm very pleased that the proposed amendments also include an expansion in the size of the Encounter Marine Park off Adelaide to include a new sanctuary zone at Port Stanvac.
"This is a win-win situation, conservation efforts would also improve with an overall increase in area protected by sanctuary zones."