The move comes after Newham Council agreed to allow an extra 50,000 plane journeys from the airport, bringing its annual flight total to 120,000.
Residents have inundated the Guardian in the past few weeks worried about noise and pollution from extra planes and changed flightpaths from Heathrow and City airport, which is less than five miles from the borough.
Lib Dem activist Kate Garrett said her group would work with apolitical campaign group Fight the Flights to leaflet residents in Wanstead and Leyton, and were hoping to organise a public meeting in the borough next month.
She said: "It seems, from listening to Fight the Flights, that there is a good case for fighting this expansion due to the procedural failings of Newham Council when granting its permission."
Conservative MP Lee Scott and Labour MP Harry Cohen have both also previously expressed concern over the issue.
A spokeswoman for Newham Council said: “Following an extensive consultation process, which included a significant amount of input from members of the public, we are confident that this decision is in the best interest of the communities of Newham."
A spokeswoman for City Airport said the allowance of extra flights by the council showed “the airport's importance in the community, its significant contribution to the local economy and the regeneration and investment that the airport has attracted to east London."