Former Lib Dem leaders Charles Kennedy and Sir Menzies Campbell are among the latest MPs to back the campaign against Air Passenger Duty.
They join 64 other MPs who have now signed parliamentary motion EDM 174 expressing concern about the impact the tax is having on families.
Their support comes as A Fair Tax on Flying’s campaign gains momentum, as 55,000 people have now emailed their MP to register their complaint about the tax.
On Friday (13 July), 40,000 emails were sent in a single day after A Fair Tax on Flying’s Twitter campaign went viral.
Meanwhile, the number of ‘likes’ on A Fair Tax on Flying’s Facebook page has just passed the 10,000 mark.
Organisers say the campaign now ranks as ‘one of the biggest social media lobbying campaigns ever organised’.
Numbers were also boosted by Virgin Atlantic, which has encouraged passengers to write to their MP after the campaign got the public backing of chairman Sir Richard Branson.
A Fair Tax on Flying dubbed the huge increase in responses as ‘the Branson effect’.
Virgin Atlantic chief executive Steve Ridgway said: ‘I hope the politicians take their constituents’ concerns seriously, and then act.’
Other high-profile MPs who have added their name to the motion include Conservative 1922 Committee Chairman Graham Brady and Select Committee Chair Keith Vaz.
Kennedy said it was ‘unavoidable that this increase will have a detrimental impact on many of my constituents’.
Another MP, Mark Durkan, who represents Foyle, has said more constituents should email him to complain about APD.
He said: ‘For me to be able to make the case to the Treasury against the current levels of the tax, I need as many people as possible to email me directly.’