A leading ecologist has quit as a NSW government advisor over a controversial plan to protect wild horses in the Snowy Mountains.
State parliament rubber-stamped the new laws on Wednesday night, which gives heritage status to brumbies in the Kosciuszko National Park.
The move has sparked outrage from environmentalists and conservation groups, and on Thursday prompted Professor David Watson to resign as a member of the state's Threatened Species Scientific Committee.
In quitting the government-appointed expert panel via a letter posted on Twitter, Prof Watson cited the legislation's "wilful disregard" for science.
He said feral horses had a "litany" of negative effects on native plants, animals, and ecological communities and were "incompatible" with protected area management.
"The government is really playing some wicked games here, pushing through legislation they know is doing harm to assets that are the property of the public," Prof Watson told AAP on Thursday.
"There are a whole lot of people out there who know a lot about horses and threatened species. Despite that clamour, they have strongly supported this bill."
The NSW Office of Environment and Heritage accepted Prof Watson's resignation "with regret".
NSW Deputy Premier John Barilaro argues the laws aimed to find a balance between managing sensitive areas of the park and managing the feral horse population through humane population control measures.
"The bill recognises for the first time the cultural heritage connection of those horses to Kosciuszko National Park," he told reporters in Sydney.
"It ends the conflict that has held back management plans and population control for decades."
If brumbies are found in highly-sensitive alpine areas, they will be relocated to other parts of the park and if population numbers grow too high, they will be rehomed through a campaign for brumby sanctuaries.
NSW Greens MP Mehreen Faruqi said it was a "rotten" plan which destroyed the national park and ignored scientific evidence.
The Invasive Species Council claims it has turned Australia "into a global laughing stock".
"It will lock in pain and suffering for the horses, which - as their numbers grow - will eat out the bush and then starve, and gives the green light to environmentally destructive management of our national parks," chief executive Andrew Cox said in a statement.
National Parks Association chief executive Alix Goodwin said it was an "international embarrassment" and vowed to fight to get the law repealed.
The state's leading animal welfare body, the RSPCA, and NSW Labor are among others who have voiced opposition to the move.
Meanwhile, the Victorian government is planning to rehome or cull about 2500 feral horses in the alpine region.
