A plan to drastically cut feral horse numbers in Kosciuszko National Park is off-track, NSW's environment minister concedes.

The brumby population in the park was to be reduced to 3000 by June 2027 but recent figures showed numbers on the rise, reaching an estimated 18,814 in November 2022.

Another 5000 horses are estimated to live over the border in the Victorian Alps.

While the previous NSW government said it was delivering wild-horse control in line with the requirements of the state's wild-horse management plan, Environment Minister Penny Sharpe chose a different tack.

"Currently this target is not on track to be met," she told Question Time on Thursday

"In fact, horse numbers have been increasing."

NSW National Parks and Wildlife staff were doing all they could and had increased the rate of removal while meeting welfare standards and safety standards, she said,

"But achieving the target will be a big challenge in that vast rugged landscape," the minister said.

"The government is working with the department to see how quickly we can deliver the plan."

Ms Sharpe also called out "absolutely unacceptable" behaviour from a small section of the community who had abused park rangers.

A federal inquiry into the alpine horse populations was told this week that people had been threatened with violence, death and workplace fire-bombing as a result of their work managing feral horses.

"Contracted professional shooters have needed to apply for intervention orders against brumby activists for having been falsely 'outed' on social media and being harassed, stalked, abused and threatened online," the Community and Public Sector Union said in its submission.

"These matters go before the courts at the contractors' own cost."

Environmental groups mostly support the eradication or drastic reduction of brumbies in the national parks due to the destructive nature of the horses' hooves to riverbanks and vegetation.

Some horse lovers however say the brumbies have an important connection to European settler heritage and government funding is needed to ramp up rehoming programs.

Wagga Wagga MP Joe McGirr has called for the repeal of the state law designating a unique heritage value to the horses, saying brumbies should be treated like any other invasive species.

He has called for a national feral horse threat abatement plan and tri-government funding for the animals' management.

"This would not be a small undertaking and would require significant consultation from communities, experts and researchers and stakeholders from around the Australian landmass," he told the federal inquiry.