Fifteen Greenpeace protesters were arrested after invading Land Rover's Solihull factory to protest at the production of " climate- wrecking" Range Rovers.
They were among 31 campaigners, dressed as staff, who breached security at the Lode Lane plant by mingling with workers arriving for yesterday morning's shift.
They chained themselves to the assembly line to stop production in the demonstration against greenhouse gas emissions.
Activists outside the plant cordoned off a black Land Rover on display at the main gates to the plant using yellow tape which declared the vehicle a "climate crime scene".
A flag bearing the words " Climate Criminal" was hoisted on a flagpole at the entrance, taking its place beside the Union flag.
The protest ended about eight hours later when 15 of the protesters were arrested.
A spokesman for West Midlands Police said: "Of the remaining 16, some were advised about their behaviour and some were advised they may receive a court summons."
Stephen Tindale, executive director of the environmental campaign group, was among the demonstrators held by police after he met for talks with plant management.
Speaking from the back of a police van, Mr Tindale, a former New Labour environment advisor, said he and senior climate campaigner Mark Strutt were arrested after a lengthy meeting with the plant manager, union convenor and head of human resources.
Greenpeace had asked the company to stop marketing off-road vehicles for urban use, to recommit to the voluntary fuel efficiency agreement it had with the EU Commission, and to withdraw from a Californian court case over the state's fuel efficiency measures.
He said: "They said they couldn't give us any assurances or commitments because they were part of the parent company and weren't senior enough, so we said 'can we speak to someone in the US' and they said 'no' and got us arrested."
A Land Rover spokesman described Greenpeace's claims as "misleading and incorrect" and said: "The action taken by Greenpeace is regrettable and damaging."