Heathrow operator BAA has denied claims it is seeking to ban millions of people from using roads and railways near the London airport.
The company is asking the High Court for an injunction to prevent a climate change demonstration later this month.
BAA's solicitor said it was aimed only at protesters who wanted to obstruct use of the airport or break the law.
But critics claim it could affect members of the National Trust, RSPB and other groups who oppose airport growth.
Those organisations could fall under the ban, opponents say, because they are affiliated with Airport Watch, an umbrella movement which unites green bodies and community groups who are against aviation expansion.
Among the critics of the proposed injunction is Mayor of London Ken Livingstone.
He has accused BAA chiefs of being "out of their skull" and said the injunction would cause chaos on the capital's transport system.
"We are only injuncting those who wish to act unlawfully"
Martin Chamberlain, counsel for Transport for London and London Underground, told the court that "until the moment we arrived at court today it was an attempt to bind five million people".
But BAA's solicitor, Tim Lawson-Cruttenden, said its ban was aimed only at "the planned direct action by environmental activists".
"We are only injuncting those who wish to act unlawfully," he said. "There is nothing to stop anyone from coming to the airport if they wish to act lawfully."
Thousands of campaigners plan to set up the Camp for Climate Action around Heathrow between 14 and 21 August.
During the camp, demonstrators want to cause disruption for the airport and its passengers.
'Servants and agents'
Mr Lawson-Cruttenden said BAA wanted only to ban those who could be deemed "servants and agents" of the camp.
He said concerns that BAA was trying to get an injunction against members of organisations that come under the Airport Watch umbrella were misplaced.
And he said the order concerned only four named people who were instrumental in protest groups.
Earlier, one of them, John Stewart, from Hacan Clearskies, said BAA was seeking "the mother of all injunctions" which was "designed to shut down peaceful protest".
"Protest is a basic British right"
But BAA says 200,000 passengers a day pass through Heathrow in August and the injunction is vital to protect their rights.
It also says it has made efforts to "facilitate lawful protest" by designating three areas on its land where demonstrators can gather.
Liberal Democrat Transport Secretary, Susan Kramer MP, joined a protest outside the High Court on Wednesday.
She said: "BAA has been deaf to the suffering of local residents who are calling for an end to plans that would double flights at Heathrow.
"It beggars belief that they are now trying to gag protest and keep objectors far from the airport.
"Protest is a basic British right. BAA needs to stop being so arrogant and start listening."
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