Between 4000 and 6000 wild horses are likely to be shot in far north Queensland in coming weeks in a campaign decried by the Save the Brumbies charity.
It follows a cull last August and September in which up to 4000 brumbies in the park were shot.
Authorities say there are too many horses in the park and they are damaging the wilderness, as well as aboriginal cultural sites.
"It's the Australian mentality," said Save the Brumbies president Jan Carter. "Fix everything at the end of a bullet.
"We are absolutely powerless to stop it."
The cull is reported to be under way in Carnarvon Gorge National Park, near the state's northern tip.
The shooting will be done from helicopter, with another following to ensure the horses are humanely killed.
Carter said aerial shooting of horses was anything but humane, and the practice was already banned in New South Wales, where she lives.
She said the ongoing culls were directly due to the failure of the federal government to implement any kind of national long-term management policy for the control, preservation and protection of the horses.
No funding was available to charities in Australian states to help in trapping and rehoming the animals.
Proposals of interest for trapping and rehoming of brumbies were sought by authorities from time to time, she said, but they were set up to fail. Without funding for trucks, yards, and staff, it wasn't viable for existing charities to undertake the work. The remoteness of some of the locations would add even further to the costs.
A recent national brumby seminar resulted in the setting up of the Australian Brumby Alliance to help provide administrative and other support to the charities in each state.
"What we are saying to the government is, we don't deny there are a lot of horses. But it is due simply to mismanagement."
"We do care about the environment," she said, but added that damage need not happen if proper brumby management was put in place.
The group proposed trapping and rehoming horses, together with fertility management through use of darts, as used in parts of the United States with some success. She said a team of experts from the US was available to come over and help set up the fertility management programme if funding was available.
Brumbies, she said, are an Australian national icon recognised internationally.
During the last Carnarvon Gorge cull, she fielded calls from media all over the world, including the BBC, Los Angeles Times, and London Times, and even from Brazil and Sweden.
Yet, she said, the cull got relatively little coverage in Australia. "It is shocking. It is just awful what they are doing."