The National Trust risks being mired in "years of conflict" if a proposal to ban trail hunting is backed by members today, countryside campaigners have said.
Tim Bonner, the chief executive of the Countryside Alliance, warned that other field sports could face bans like grouse shooting and fishing.
There are already talks about a new campaign among environmentalists to ban grouse shooting on two National Trust moors in Derbyshire.
Baroness Mallalieu, the alliance's president and a member of the National Trust, added that "from being regarded as the custodian of our countryside, the charity is well on the way to being seen as the manager of a bland and sanitised theme park".
As many as 500 members are expected to attend to vote in person at the meeting today in Swindon. The vote was open to the Trust's five million members.
Mr Bonner told The Daily Telegraph: "Any decision to ban trail hunting on National Trust land would launch years of conflict within the Trust as hunting members seek to reassert the right to hunt on land which has been hunted for generations.
A decade of hostilities between the Trust and its tenants and closest supporters would be an inevitable consequence of being bullied by online campaigners
Simon Hart MP, former chief executive of the Countryside Alliance
"There would undoubtedly be a motion to overturn any ban at next year's AGM and with the time and opportunity hunts will engage thousands of activists.
"The fall out from the Trust's decision to ban stag hunting in the West Country lasted for years and the move to prohibit all hunting would be much more fundamental.
"Hunts have survived the hunting ban and everything else that has been thrown at them. They are not going to bow to a few thousand activists who have no understanding of the importance of hunting in the countryside.
"If the Trust did bow to this prejudice campaign and ban hunting it is already clear that there will be motions to ban shooting, fishing and anything else that offends animal rights sensibilities in future years."
Lady Mallalieu added: “The National Trust has got itself into a mess by involving itself in political issues which have little or nothing to do with its core purposes, embracing political correctness and running scared of digital campaigning and harassment by sometimes very small vocal pressure groups.
Simon Hart, a Tory MP and a former chief executive of the Countryside Alliance, added: "A decade of hostilities between the National Trust and its tenants and closest supporters would be an inevitable consequence of being bullied by online campaigners."
But Philippa King, the acting chief executive of the League Against Cruel Sports, said: “This issue is not about eradicating tradition. If people want to hunt – legally – they can do so by going drag hunting, which is a non-lethal sport with 200 years of tradition, and which will not be prevented by this motion.
"The only thing people are trying to stop is the illegal and cruel hunting of foxes, hare and stags under the disguise of ‘trail hunting’.
"National Trust land should be available for everyone to enjoy – but killing animals for fun is no longer an acceptable countryside pursuit. If some people cannot find enjoyment in anything other than killing for sport, then the problem is with them, not with those who want to live in a compassionate society.”
A National Trust spokesman said: "As we’ve set out in our response to the annual general meeting resolution, the Trust licences responsible trail hunting on its land.
"Members will have the opportunity to vote on and discuss trail-hunting and the A303 at Stonehenge during the AGM."
The spokesman said there had been no change on the Trust's approach to grouse shooting.