(CNN) -- Environmental campaign group Greenpeace has called for people to join a "global day of solidarity" Saturday for 30 people detained and charged with piracy by Russia as they protested Arctic drilling last month.
Russian authorities made the arrests after two of the activists left the Greenpeace icebreaker Arctic Sunrise and tried to climb the side of an oil platform owned by the Russian energy giant Gazprom in the Barents Sea.
Greenpeace has condemned the Russian action, saying its activists were taking part in a peaceful protest against the "slow but unrelenting destruction of the Arctic."
The group has called on supporters around the world to stage candlelight vigils Saturday, holding signs saying "Free the Arctic 30," to highlight the plight of those detained.
All 30 people aboard the ship, including 28 activists and two freelance journalists from at least 18 countries, were charged last week with piracy.
Meanwhile, the government in the Netherlands -- where the Arctic Sunrise is registered -- wrote to the Dutch parliament Friday to say it has launched legal action aimed at freeing the 30 under the UN Convention of the Law of the Sea.
"With regard to its detention of the ship, Russia invokes its authority to ensure safety at sea in the vicinity of the oil platform," Dutch Foreign Minister Frans Timmermans wrote. "The Netherlands agrees on the importance of safety at sea, but in this case we contest the lawfulness of detaining the ship and its crew."
The "arbitral procedure" it has filed focuses "on what the Netherlands views as the unlawfulness of boarding and detaining the ship and on our demand for the release of the ship and its crew," it said.
"Under this procedure the Netherlands can in two weeks, if insufficient progress has been made, request the International Tribunal for the Law of the Sea to prescribe provisional measures for the release of the ship and its crew."
This would not interfere with Russia's ability to pursue criminal proceedings against the 30 people, Timmermans said.
Two of those detained are Dutch nationals, both of whom are receiving consular assistance.
The defendants also include Americans Peter Wilcox, who is the captain of the Arctic Sunrise, and Dmitry Litvinov, who Greenpeace says also holds Swedish citizenship.
The other detainees are from Argentina, Australia, Brazil, Canada, Denmark, Britain, New Zealand, Ukraine, Russia, France, Italy, Turkey, Finland, Switzerland, Poland, the United States and Sweden, the group said.
None of those charged last week pleaded guilty, Russia's Investigative Committee said. If convicted, they could be sentenced to up to 15 years in prison.
Lawyers acting on Greenpeace's behalf have filed appeals in court seeking the defendants' release, Greenpeace said Thursday.
Greenpeace International's General Counsel Jasper Teulings said Friday he welcomed the Dutch government's "strong stance in support of the rule of law and the right to peacefully protest. Russian officials will now be called to explain their actions before an international court of law, where it will be unable to justify these absurd piracy allegations."
Russian authorities accuse the defendants of trying to commandeer the platform.
The authorities and Gazprom also say the activists endangered the lives of the company's employees and that their action could have led to an environmental disaster.
CNN's Bharati Naik, Alla Eshchenko and Jill Dougherty contributed to this report.