The so-called "Arctic 30" were arrested by Russian authorities Sept. 18 after two Greenpeace activists tried to scale the side of an oil rig operated by the Russian energy giant Gazprom.
The 30, which included volunteers and crew members from South America, Europe, Australia and New Zealand, as well a Russian freelance photographer and ship cooks from Turkey and Ukraine, were jailed in Murmansk on piracy charges.
After international pressure, a Russian court reduced the piracy charges -- which carry a maximum 15 years in prison -- to hooliganism, NBC News reported. If convicted of hooliganism, the activists could spend a possible seven years in prison.
Defense lawyers for the activists said they plan to request all charges be dropped, RIA Novosti reported.
"We consider the hooliganism charges as absurd as the piracy ones, because the activists did not carry out any actions violating public order," Greenpeace spokesman Mikhail Kreindlin said.