A huge rise in house building in the West Midlands' countryside threatens green belt land and is "environmental vandalism", campaigners have claimed.
Urban authorities say they have limited building land
The Campaign to Protect Rural England (CPRE) fears the region is the new "battleground" for housing development due to increased government pressure.
Government predictions could see 50% more land than currently planned being allocated over the next 25 years.
The government, and housing charity Shelter, have rubbished the claims.
The West Midlands Regional Assembly is consulting councils about the plans for housing development.
Urban authorities say that they have limited building land and developers would abandon house building on derelict or under-used sites that need remedial work if they were given cheap greenfield alternatives.
Shropshire and Herefordshire councils have told the assembly they cannot meet the predicted figures without serious damage to the countryside and market towns.
But Worcestershire County Council is contemplating expanding Worcester and Redditch into the countryside and Coventry and Warwickshire have not ruled out sacrificing areas of green belt for expansion.
Burton-on-Trent, Hereford, Rugby, Shrewsbury and Telford - all already targeted for development - could also be involved.
Lichfield, Warwick and Leamington, which have been growing fast in recent years, would have to keep on growing to fulfil the higher numbers.
The CPRE said the government's belief that building more houses will reduce prices is misguided.
It is not convinced that the house building industry would build at the much higher rate and believes developers could end up cherry picking the most profitable green field sites.
The exodus of people from the city to the countryside would accelerate, the CPRE believes, undermining efforts to make areas like East Birmingham, the Black Country and North Staffordshire more desirable places in which to live.
Peter Langley, vice chairman of West Midlands CPRE, said: "The West Midlands needs more affordable homes but swamping the market with greenfield land and playing fast and loose with the region's long-established green belts won't achieve that; it's a form of environmental vandalism.
"The Regional Assembly must stick to its guns and resist government pressure to open the floodgates to new housing."
A spokeswoman for the department for communities and local government said: "The CPRE claims are absolute nonsense.
"We need to build more homes in every region but our record over the last nine years shows we can increase building on brownfield land and protect the green belt."
Three-quarters of all new homes in the West Midlands were already built on brownfield sites and thousands more hectares of such sites are still to be used, she added.
"If we don't build more homes then only a third of today's ten-year-olds will be able to afford a place of their own in 20 years' time," the spokeswoman added.
Shelter's director Adam Sampson said: "It appears the CPRE is continuing to peddle myths about the level of housing demand and is still wedded to the idea of a rural housing system frozen in time.
"Action is needed to provide both social housing and more private homes to ease the crisis in housing supply and affordability."