Hearings triggered by Lydd Airport Action Group and the RSPB take place next week – and if judges find in their favour, it could lead to another public inquiry.
The RSPB's appeal will be heard at the Royal Courts of Justice in London next Tuesday and Wednesday and LAAG's will be heard as a separate case on the following two days.
Chris Sproul of the RSPB demonstrating against the airport outside the Civic Centre in Folkestone
Their case will be over the legal process rather than the merits of the scheme.
An RSPB spokesman said: "Our hearing will be on legal grounds, whether due process was followed in the public inquiry.
"If the court finds in our favour it could mean another public inquiry. If that means time and money, so be it, because we never believed this development was right in the first place.
"We did not feel that the environmental issues were taken fully into consideration."
LAAG co-ordinator Louise Barton said: "Our issue was different to the RSPB's as it was on nuclear safety. But this hearing is not looking at the merits of the case for or against expansion but the decision that was reached.
"We want the High Court to quash the decision as null and void.
"If it does lead to another public inquiry it would be on a smaller scale than the last one as there would be a more limited subject range.
"It would just be a question of another inspector reviewing the evidence."
LAAG did not want to disclose further details of its case until the court hearing.
Lydd Airport won planning permission for the £25 million development last April 10 from both Transport Secretary Patrick McLoughlin and Communities Secretary Eric Pickles.
It was for two applications – one to build a 294-metre runway extension plus a 150-metre starter extension for aircraft manoeuvres.
The other is for a new terminal for 500,000 passengers a year.
Demonstraters against the expansion of Lydd Airport outside the Civic Centre, Folkestone
The public inquiry was over seven months from February 2011 at Folkestone's Civic Centre.
The RSPB had argued about the risk to wildlife, but LAAG argued over dangers because of the closeness of the Dungeness nuclear complex.
A Green MEP said the court action is a fightback against a government "hell-bent" on airport expansion.
Green Party MEP Keith Taylor in New Romney
Keith Taylor, Green MEP for the South East, said: "Any expansion of Lydd airport, in an area of global importance for wildlife and next door to a nuclear power station, is clearly bad news.
"The government is hell-bent on airport expansion but local people, whose lives will be blighted by increased pollution and noise, are right to stand up against these plans.
"We know that airport expansions will contribute to climate change, and we know that a larger airport at Lydd will threaten both the wildlife in the area and the peace and quiet enjoyed by local people.
"Lydd airport expansion shouldn't go ahead and I wish campaigners the best of luck in their legal challenge to the government’s ideological obsession with expanding airports at any cost."
Folkestone and Hythe MP Damian Collins, a supporter of the airport’s expansion said: "I don't think there are any grounds for appeal.
"The planning inspector upheld the application and went through all the evidence in great detail, finding no grounds not to give permission.
"The point of a High Court hearing would be to whether the decision was flawed and I cannot see any grounds for that.
"Lydd Airport is confident that there are no grounds for appeal and are happy to continue with their plans for the airport.
"There is no point in in continuing a debate that has been heard in great detail."
Lydd Airport said it did not want to comment at this stage.