Campaign group Back Heathrow believes that if expansion was put to a direct vote in the Commons, 150 Labour MPs would side with the government and vote for a third runway.
A parliamentary vote on Heathrow has been promised by the government before the summer recess.
The event was jointly hosted by Unite the Union and Back Heathrow, who intending to send a signal to Theresa May's government to call for a vote on the expansion project.
Ealing Southall MP Virendra Sharma spoke at the event, saying: “We cannot miss this opportunity to expand Heathrow – Britain’s hub airport is an engine for growth and if London is to thrive we must grasp the opportunity and expand it responsibly.
“Heathrow expansion will create thousands of new jobs in Ealing and tens of thousands across London. Subsequently, there will be many more people spending money in the local economy, meaning more jobs and success for local small businesses.”
Heathrow Airport is currently running a mega-consultation on how the airport could work and operate as well as the future of the M25 and future rail links.
The Commons transport select committee has finished hearing evidence and is expected to publish recommendations for the government's National Airports Statement.
Back Heathrow estimates expansion at Heathrow will create 180,000 jobs nationwide and 10,000 apprenticeships, however many residents around Heathrow have continued to express concerns over noise and environmental impact of expansion.
Executive director of Back Heathrow, Parmjit Dhanda said: "This event shows that we effectively already have a majority in Parliament for expansion at Heathrow and the green light for 180,000 new jobs.
“We are confident that over 150 Labour MPs would join forces with the government to push through this crucial infrastructure decision. Mrs May needs to get on with it."
A London Labour Party spokesman said: “Labour supports airport expansion in the South East – it is vital to Britain’s economic success.
"Our support for Heathrow has always been conditional on four tests being met: on capacity, climate change, noise and air quality and the wider national benefits.
"A Labour Government will carefully consider all evidence against these tests before making a decision in the best interests of our country.”
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