Campaign to Protect Rural England has warned the Government to reject calls to build on the Green Belt.
Shaun Spiers, Chief Executive of CPRE, said reports that senior ministers are contemplating a new Bill to sweep away planning controls are "deeply worrying".
He also warned that coalition MPs will resist any moves to build on England's 14 Green Belts.
The protected areas around towns and cities cover around 13% of the land and 88% of the population lives in the urban areas within Green Belt boundaries.
A recent report from Policy Exchange said the planning system is dysfunctional and claimed 70% of people would be happy to see building on Green Belt land.
"It is little consolation to a child growing up in a dense, grey, inner city that miles away on the urban fringe there is little more intensive farmland than there otherwise might be," the report said.
"People believe that the green belt is national parks and forest, yet the majority of green belt does not consist of meadows or nature reserves but intensively farmed land around cities"
Mr Spiers said:
"There have been three significant reforms of the planning system since the coalition took office, and ministers should give them time to take effect rather than embarking on yet another upheaval.
"As for the idea that Green Belt protection needs to be weakened to boost economic growth, the Government has made clear time and again that it will protect the Green Belt, and any attempt to weaken it will go down very badly with Government MPs.
"In fact, there is growing evidence of harmful new development being promoted within the Green Belt. The Green Belt needs to be strengthened, not weakened."
Mr Spiers said there is no evidence that the planning laws are restricting the building of much-needed new homes.