Calls to halt the government aviation white paper have been made after a study concluded that two other options should have been considered.
An airport at Cliffe is one option the government has suggested
The study, for a local authority group, says the government should have looked at building airports at Sheppey and at Thames Reach, east of London.
Publication of the government white paper is due in less than two weeks.
The government consultation has been criticised as "loaded in favour of piecemeal and unrelenting expansion at existing sites".
The consultation listed one new airport proposal at Cliffe in Medway, which environmentalists have opposed.
The study was prepared by aviation economic specialists Berkeley Hanover for the Strategic Aviation Special Group (SASIG) of the Local Government Association.
SASIG chairman Richard Worrall said the consultation "did not give the public the chance to consider whether a brand new airport in an area where very few people would be affected might be the answer.
"Ministers knew when they published their revised consultation paper in February this year that both Sheppey and Thames Reach were closer rivals to Heathrow than Cliffe - but still they left them out."
He added: "This country needs a new airport if we are all to enjoy the benefits of flying without destroying the lives of residents around Heathrow, Gatwick and Stansted."
He said an airport in the Thames Gateway Growth Area was "the ideal location".
Legal advisers for the group have now written to Transport Secretary Alistair Darling calling on him to halt the publication of the White Paper, which is due out in less than two weeks.