A joint legal battle against plans to expand Heathrow Airport will be heard at the High Court.
Local authorities in London and campaign groups including PlanB and Friends of the Earth are challenging the government's decision to approve the building of a third runway at Heathrow.
The case is being brought against transport secretary, Chris Grayling, with those opposed to the plans claiming the project fails to properly deal with the impact on air quality, climate change, noise and congestion.
Mr Grayling said the new runway would set a "clear path to our future as a global nation in the post-Brexit world".
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Construction could begin in 2021, with the third runway operational by 2026.
However, Mayor of London Sadiq Khan said: "Heathrow expansion will result in hundreds of thousands of people being blighted by intolerable noise levels and worsening air quality in an area where pollution is already well above legal levels.
"The Government has failed to demonstrate how it will fund the billions of pounds needed to improve road and rail connections to the airport."
We will 'robustly defend our position'
A Department for Transport spokesperson said: "As with any major infrastructure project, we have been anticipating legal challenges and will robustly defend our position.
"Today's hearing does not impact on the work Heathrow is undertaking on its application for planning consent or the timetable to deliver this much-needed runway."
The case will be heard at the High Court on Thursday.