Labor says the future of the Great Barrier Reef is on the line, as it opposes new government plans to regulate marine parks.
On Wednesday, the government introduced changes to the regulation of 44 Australian marine parks, covering 3.3 million square hectares, that would reduce 'green' conservation areas in the Coral Sea from 50 to 25 per cent.
Labor says this removes "more area from conservation than any other government in the world, ever".
"They say they've got a good conservation outcome - that's true if you're not a fish," Labor environment spokesman Tony Burke told ABC radio on Wednesday.
"Imagine for all the national parks we have on land if at the stroke of a pen the government said, 'They're all still national parks but you can walk into half of them and shoot the wildlife'."
Labor will move to disallow the changes in both houses of parliament.
But Environment Minister Josh Frydenberg is adamant the new plans strike the right balance.
"This is achieving the best possible balance through an effective and targeted approach to get good economic and good environmental outcomes," he told the ABC.
Mr Frydenberg admitted five million recreation fishers would get more access to Australia's marine parks.
"That is consistent with having a healthy ecosystem and enhanced biodiversity," he said.
World Wildlife Fund Australia said the changes would send Australia's conservation reputation "from the penthouse to the outhouse".
"This expanse of ocean beside the Great Barrier Reef is the Serengeti of the Sea - still largely untouched," the environmental group's head of oceans Richard Leck said in a statement.
"Now it will be open slather for destructive commercial fishing activities like trawling, gillnetting and longlining."
Liberal Senator Anne Ruston told reporters Labor's 2012 marine park plan was "unscientifically designed" and "unconsulted".
She said the government's changes ensured people "who want to throw a line over the side of their boat, people who want to feed their children Australian seafood for dinner tonight will still be able to get access to our world-class sustainably managed seafood".
Labor will need crossbench support for its disallowance motion to succeed.
Crossbench Senator Derryn Hinch indicated he was concerned about the changes, particularly around the Coral Sea, and said he wanted to get extra protection for sea turtles and dugongs.
