The UK's National Union of Rail, Maritime and Transport Workers (RMT) is urging the government to divert millions of pounds from planned investment in Heathrow into improving of the country's rail network.
The government is planning a third runway at the west London airport.
An RMT study said thousands of jobs would be created and pollution would fall if rail was prioritised, the BBC reports.
The report said over a third of flights from Heathrow are short-haul, more than 20% go to destinations already served by a viable rail alternative, and one in five more are to places where rail is a potential alternative.
A Department for Transport spokeswoman said "some people will need to fly because they are using Heathrow as a connection to another country".
"Unilateral action to constrain growth at Heathrow means passengers simply choose another airport for their onward flight. This doesn't save carbon, it just costs jobs."
By staff writer
