London Mayor Ken Livingstone has urged Heathrow Airport authorities to rethink plans to curb a climate change protest.
Protesters are keeping the location of their encampment a secret
Operator BAA is seeking an injunction to curtail a week of action starting on 14 August by environmental groups opposed to the airport's expansion.
The mayor said he would oppose the injunction in court because it would cause havoc on the Tube and buses.
BAA has said it is seeking the ruling "to protect the operation of the airport and the safety of passengers".
Mr Livingstone said the injunction would bar protesters travelling to Heathrow in west London from using the Tube or London buses.
He said enforcing the ban, which would involve police surveillance, stop and searches and arrests, would cause disruption to transport.
Mr Livingstone said: "It is extraordinary and unacceptable that BAA did not consult Transport for London (TfL) about this proposed injunction, which could have a serious impact on underground services.
"Instead of protecting the public from anyone bent on violence or disruption, this injunction targets potentially millions of people," he said.
He said BAA's actions had only succeeded in raising the public's awareness of the protest, which would have been handled adequately by police.
"Now it will undoubtedly be more large than it would have been," he said. "Someone there must be out of their skull.
He said BAA's management of the planned protest was "an example of breathtaking stupidity".
Mr Livingstone has asked BAA to remove all references to TfL property and services from the injunction.
He added that TfL "will oppose in the courts any attempt to restrict the lawful use of its public transport services".
Direct action by "green" groups under the banner Camp for Climate Change is planned between 14 and 21 August.
Organisers claim up to 5,000 people will take part, spending a week in tents outside the airport.
BAA said faced with some activists' publicised plans to "disrupt and blockade" the airport through direct action, it had no alternative but to apply for an injunction.
The operator said it needed to strike a balance between the right of passengers to travel unhindered and the right to protest lawfully.
"We respect people's democratic right to protest lawfully," said a BAA spokesman. "One of the purposes of the injunction is to facilitate lawful and peaceful protest."