Countryside campaigners have warned that government housebuilding plans threaten the "quality of life" in the South East.
The CPRE is worried the government will step up building rates further
The Campaign to Protect Rural England (CPRE) has written to Tony Blair and John Prescott with its complaints.
The group backs growth in the Thames Gateway region, but remains "seriously concerned" about housebuilding plans for another three zones.
Soaring house prices and a chronic housing shortage led to the plans.
Deputy Prime Minister John Prescott named the sites on which more than 200,000 homes would be built in his £22bn Sustainable Communities Plan last July.
He argued that key workers such as teachers, nurses and firefighters needed low-cost affordable homes but were being pushed out of the market by London's soaring property prices.
Other than the Thames Gateway - stretching from east London into parts of Essex and Kent - the areas to be developed are Ashford in Kent, the Cambridge-Stansted M11 corridor and around Milton Keynes.
The CPRE is urging the prime minister to resist calls to raise the housebuilding rate still further.
Chief executive Shaun Spiers said: "There's a lively debate going on within the government as to whether it need concern itself with the future of the new urban communities that will be created through its housebuilding programme.
"We think it's absolutely critical that urban regeneration, countryside protection and liveability do not take a back seat in a housebuilding numbers
game," he said.
In his letter Mr Spiers said they had concerns about large-scale greenfield development and the "impact it would have on the quality of life in south-east England".
These concerns had been "amplified", he said, by the government's "apparent acceptance" of proposals set out in a recent housing supply review, recommending a further increase in housing provision.
The Treasury-sponsored Barker Review said Britain needed to build up to 140,000 extra new homes a year if housing supply was to match demand.
The CPRE also said it remained concerned about the government's belief in the plan as a solution to rising house prices.
It said research carried out as part of the Barker Review showed the anticipated scale of building would have very little impact on prices.