Australia’s environment laws are suffering a “death by a thousand cuts”, conservationists have warned, after the government unveiled plans to amend the key legislation that protects endangered species.

Greg Hunt, the environment minister, has put forward a bill that would mean he would suffer no recourse if he approved major developments without taking expert advice.

The bill adds a clause to the Environment Protection and Biodiversity Conservation Act which states that a decision to approve a development will not be invalid “merely because the minister failed” to receive “relevant approved conservation advice”.

The government said the move was prompted by a court challenge by environmentalists to a proposed mine in north-west Tasmania. The court ruled the project could not continue until the government considered advice on harm caused to the Tasmanian devil, which Labor’s then environment minister, Tony Burke, had failed to do.

The Coalition’s change would mean this, and similar, legal challenges to approvals would fail.

While the environment minister will still be required to consider expert advice, there will be no penalty for failing to do so.

Jess Abrahams, the healthy ecosystems campaigner at the Australian Conservation Foundation, told Guardian Australia that Hunt was reducing his accountability to protect endangered species.

“These are weasel words, in many ways, because the minister can ignore advice with no recourse at all,” he said. “Review and recourse from third parties to government decisions is an essential part of democracy, so it’s very worrying this is being removed.

“Environmental protection is suffering a death by a thousand cuts at the moment. Laws are being weakened and approvals are being handed over to the states, which have a questionable record of protecting the environment.

“We won’t let this one go. It’s part of a much bigger attack on environment laws. We should be strengthening laws as the Environment Protection and Biodiversity Conservation Act is far from perfect, but instead we are watering them down.”

Conservationists say the amendment would stymie a challenge to the Maules Creek mine in NSW, which they say was approved based on erroneous information.

Whitehaven Coal, the mine’s developer, was allowed to clear 544 hectares of endangered box gum woodland, as well as further habitat that contains threatened species such as the swift parrot and greater long-eared bat. Hunt is being urged by conservation groups to revoke the approval.

Hunt is also set to decide whether to allow the dredging of 3m cubic metres of seabed to allow the expansion of the Abbot Point port in Queensland. Advice released by the previous Labor government indicated that dumped sediment travels far further than previously thought, posing a potential threat to the Great Barrier Reef.

Mark Butler, Labor’s environment spokesman, told Guardian Australia: "This is just further evidence of a government that quashes debate and refuses to listen to the experts.

"First they shut down the bodies providing advice on climate change; now they want to ignore conservation advice too."

The Greens also attacked the plan. “The Abbott government is putting in place the legal framework to silence community opposition to its agenda of coal and gas at all costs,” said the Greens senator Larissa Waters.

“With many of our most loved species on the brink of extinction, including the leadbeater’s possum, Tasmanian devil and bilbies, we should be strengthening their protection not tearing it apart.”

But Hunt’s spokesman told Guardian Australia that the move didn’t lessen protections.

“The requirement for the decision maker to have regard to any relevant approved conservation advice is maintained,” he said.

“The amendments apply to ensure that past decisions which have been made are not at risk of being invalid. The amendments will provide certainty for industry stakeholders with existing decisions and the projects that rely on those decisions.”

The government is also toughening up penalties for the illegal killing, trading and keeping of sea turtles and dugongs.

Fines for these offences will be tripled, with the government working with Indigenous elders to stop the practice.

“The government will not tolerate illegal poaching of dugongs and turtles under the cover of traditional hunting,” Hunt’s spokesman told Guardian Australia.

The ACF’s Abrahams welcomed the move but said wider threats to marine creatures needed to be addressed.

“It’s great that illegal hunting is being targeted, but is that the real threat that dugongs and turtles face?” he said. “Let’s look at the real cause of the losses to these animals, such as the industrial development that has destroyed the seagrass that dugongs and turtles feed upon.

"We need to look at the bigger picture, which is the loss of habitat.”