Persimmon Homes, Britain's third-largest housebuilder, has been targeted by a militant underground group furious with its plans to build 10,000 homes on a green belt site west of Stevenage in Hertfordshire.
Urgent - the Urban Regeneration and Greenfield Environment Network - is to protest against what it says is Persimmon's "poor" record on the green belt at the company's annual general meeting in April. Urgent has threatened more militant action on the day if its views are not aired.
The network recently bought 500 shares in Persimmon and is giving away one free share - worth around pounds 2.10 - to every environmental campaigner who buys a copy of its newsletter. It has already passed 200 to supporters.
Although the group admits it has no chance of directly affecting voting at the meeting, it aims to persuade other shareholders to join calls for motions to rule out the company's involvement in green belt housing developments.
Ali Brown, a member of Urgent who bought a share last month, said he believed it was in Persimmon's interests to heed the voice of its new members. He said: "Housebuilders in general are going to come in for quite a lot of stick in the next few years as they start building houses on beautiful pristine land and start making that land less beautiful.
"The first major housebuilder who decides to build exclusively on brownfield land rather than trash the green belt will clearly gain a decisive market edge over its competitors. As a shareholder in Persimmon, I want to see the company in which I have a financial interest do well. At the moment, they risk being associated with the destruction of the countryside, and that is a dangerous route to go down."
Mr Brown also said he believed the company's record of building on green belt land - as opposed to already-developed brownfield - to be poor. "Persimmon's name just keeps coming up time and time again when people talk about green belt under threat," he said.
Urgent is fast acquiring a reputation as a proactive and militant organisation. It recently occupied offices of another developer of expensive homes, Bryant Country Homes in Oxford, and orchestrated a raid on the offices of the Construction Confederation last year.
A spokesman for Persimmon said members of Urgent would, as shareholders, be free to attend the AGM but warned that anyone who was disruptive would be ejected and police would be called if necessary.
Persimmon, owned by the multi-millionaire Duncan Davidson, is believed to claim that more than half the land it develops is brownfield and has created itself a marketing niche in such sites.
The Government wants 4.4 million new flats and houses built by 2016; it has said that 60 per cent are to be on former industrial sites. But there are fears that the drive to encourage developers to build on old industrial land will expose increasing numbers of householders to the risk of poisoning from contaminated land.
Last year, Persimmon was ordered to stop developing a former railway depot after Oxford City Council said the developer's policy "could cause environmental pollution and present a public health risk". It claimed Persimmon breached its remit by pursuing the second phase of development before approval was given to measures to make the site safe. Oxford's director of environmental services called Persimmon's policy short-sighted.
The decision to provide up to 10,000 homes on green belt land west of Stevenage was taken by the local authority. Persimmon said it has never targeted green belt land, but local, more orthodox protesters in Stevenage said they had some sympathy with Urgent campaigners.
John Davies, a spokesman for the Campaign Against Steven-age Expansion, said: "Our main concern is with the local county council, whose policy we believe is deeply flawed. But Persimmon just cannot believe their luck at being given more than two square miles of pristine green belt to build on."