The six bodies including the Campaign to Protect Rural England, the Campaign for Better Transport, Friends of the Earth and Sustrans, have spoken up ahead of a consultation on the eco-towns initiative to call on the government to restart the process.
The letter calls on Flint to scrap the current shortlist because the sites would be very car dependent.
Its authors are particularly concerned that the shortlisted sites will have poor rail links and that they will effectively become commuter towns dependent on car use for around 95% of journeys. It calls for large brownfield sites within existing urban areas to be considered for eco-towns.
"One of the main criticisms of this initiative, from experts and a range of interests, not just environmental groups, is that schemes will become car dependent commuter towns," says the letter.
"We urge you to consider the role eco quarters on larger development sites could play in raising environmental standards in existing towns as has been suggested for Thames Gateway."
The letter calls on the Department of Communities and Local Government (DCLG) to:
Compare shortlisted sites with brownfield sites in urban areas
Reject all shortlisted sites if they fail key tests on transport, particularly rail links
Subject sites to local authority Regional Spatial Strategies and Local Development Frameworks
Reject the schemes if they fail these tests
Campaign for Better Transport director Stephen Joseph told NCE that the reaction from DCLG to the letter had been constructive.