Greenpeace says it will challenge any efforts by Russian authorities to bring criminal charges against 30 crew members, including two New Zealanders.
The crew of Arctic Sunrise have been detained while their vessel is being held outside the port city of Murmansk.
Greenpeace New Zealand executive director Bunny McDiarmid says the crew were taken by bus to the offices of the Investigative Committee of the Russian Federation on Tuesday.
The Arctic Rise was circling an oil rig in the Barents Sea to protest against drilling by Russia's state energy agency, Gazprom, when it was boarded by armed officers and detained.
A federation statement says activists had tried to board the oil rig illegally and their actions had threatened the ecological security of the area.
It says the oil rig was carrying electronic material and unauthorised activity could cause an accident.
Ms McDiarmid says no formal charges have been laid yet and piracy charges would be very hard to prove.
"Piracy would have no merit under the legal definition of piracy. It has to be a violent act for private means, which is not what happened."
She says the two New Zealanders involved have had limited contact with their families but are in good spirits.