Uttlesford District Council and Manchester Airports Group have until Friday (May 7) to tell the government what they think about Stansted's expansion plans.
MAG wants to increase the airport's capacity, a move rejected by Uttlesford District Council.
They then took the application to the Planning Inspectorate on appeal last summer.
A change in climate laws last month now takes into account emissions from international flights for the first time, leading the Planning Inspectorate to open up a new window for comments.
UDC, MAG and campaign group Stop Stansted Expansion, which is due to change its name to Stansted Airport Watch, are among the commenters.
The plans under appeal include new taxiways and aircraft stands.
The airport wants to accommodate 43 million passengers each year. The current capacity is 35 million passengers.
The new climate laws aim to slash emissions by 78 percent by 2035.
Stansted Airport said: "We will respond as appropriate and necessary within the stated timeframe."
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