Disillusioned members feel the trust's problems have become so serious that they have formed a breakaway organisation - Friends of the National Trust (Font) - to return it to its core aims - to preserve and conserve the nation's heritage.
The group says it already has 3,000 members and that more people are joining every day.
Charles Collins, a life member of the trust, who founded Font with Richard Clegg QC, Baroness Ann Mallalieu QC and Tim Cassell QC, said the trust had an increasing tendency to make decisions based on short-term commercial expedience rather than common sense and expert advice.
"We have heard from tenants living in villages bequeathed to the trust who say the trust is ruining traditional village life by selling houses to commuters and as holiday lets. And we just feel that it has become too large and too greedy.
"Why do they need to spend pounds 3m buying Snowdonia when it was already being preserved and conserved by the National Parks Agency? The perception is that they will end up developing it with their shops and car parks and the money would have been much better spent preserving houses or buying art and treasures," he said.
Font was also concerned, he said, that the trust had banned deer hunting on the Holnicote Estate in Exmoor, a decision that disregarded the express wishes of Sir Richard Acland, who donated the land.
"By ignoring the memoranda of wishes, which is about what the donor wants and is morally, if not legally, binding, the trust is making up the rules as it goes along. It has become authoritarian.
"We are all very enthusiastic member and appreciate what the trust was set up to do,but we feel that its decisions are off line at the moment," he said.
As part of its campaign for reform, Font has tabled three resolutions for consideration at the trust's annual general meeting in November.
It has nominated seven candidates to stand for election to the trust's council, including Lucinda Green, an Olympic gold medallist.
The trust banned hunting in April 1997 after a report by Professor Patrick Bateson, which found that pursuit by dogs and people on horseback was grossly stressful, exhausting and agonising for the red deer of Devon and Somerset.
But Mr Clegg said the trust had violated its agreement with Sir Richard who bequeathed his land on the understanding that deer hunting would be permitted on the estate for as long as it continued on neighbouring land.
"Hunting has not been banned by law and the trust has reneged on the specific wishes of Sir Richard. They had no right to do that and we feel the situation should be reversed," he said.
Baroness Mallalieu also has submitted a resolution to the meeting, saying the trust is pursuing a policy of selling property and land for commercial development, which brings it into direct conflict with environmentalists and the trust's neighbours and supporters.
"Those of us who support the aims of the trust to protect and preserve our heritage are greatly saddened to find that it is increasingly seen as an enemy of the countryside instead of its champion. Resentment against the trust is now country wide," she states.
A spokeswoman for the National Trust said it could not approve of Font's call for the reintroduction of deer hunting. "Any organisation as large as the trust is bound to have dissentions and disagreements and it is proper that people should be able to voice their opinions," she said.