Heathrow spent more than £2m advertising on London’s tubes and buses in 2015, according to Mayor of London Boris Johnson.
It spent £256,854 on advertising on Transport for London in November and £282,803 in December.
Hacan chairman John Stewart accused the airport of attempting to “buy” a new runway.
He said: “When one side can spend this amount of money to get across its view, it is not a level playing field.
“In many ways, Heathrow is buying a new runway.”
Heathrow has been contacted for a comment.
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