Campaigners have submitted an application requesting a judicial review to the High Court
The news comes as plans to expand the runway by 164m were approved by councillors at Eastleigh Borough Council in April after days of debate.
The council previously said it was confident that its decision-making process was sound.
But since last month campaigners have raised more than £35,000 to fund legal action.
It comes as they called for the decision to undergo ‘independent scrutiny’.
Richard Mould-Ryan from Airport Expansion Opposition Southampton (AXO) said the runway expansion would have ‘far-reaching consequences for the climate’.
He added: ‘We believe strongly that the council’s decision was wrong both in the way it was taken and the arguments to justify it. The airport has greatly overstated the economic benefits of expansion, whilst hugely underplaying the environmental impact. Decisions such as these need full scrutiny and that can now only happen by judicial review.’
Campaigners said they were confident that they would be granted permission for a full judicial review.
Steve Szalay, operations director at Southampton Airport, said: ‘We are hugely disappointed by their decision to bring legal action, particularly given that nearly 4,800 local people wrote to express their support for the plans. The runway extension is a key part of our plans for the future of the airport and will deliver significant economic and employment opportunities to Eastleigh and the central south. Unfortunately, this legal challenge activity will delay the creation of much-needed jobs at a time of high post-pandemic unemployment.’
Mr Szalay said he was committed to the runway extension plans.
He added: ‘In light of the extensive scrutiny and public consultations undertaken by Eastleigh Borough Council, we are confident that the courts will back the council’s decision to approve the runway application.’
Eastleigh Borough Council was approached for comment.