Russian authorities turned their informal descriptions of Greenpeace activists as pirates into legal charges Wednesday, a chilling evolution in a saga that began as a protest against drilling in the Arctic.

Prosecutors charged 14 people — including a British journalist — with piracy, which carries a maximum penalty of 15 years in prison.

Two weeks ago, the American captain of the Greenpeace ship Arctic Sunrise, who is among those still awaiting charges, sailed near an oil rig in the Pechora Sea owned by a subsidiary of Gazprom, the energy giant controlled by the Russian government. Activists in inflatable boats approached the platform, and two were detained as they tried to climb onto it and raise a banner.

The next day, members of the Russian Coast Guard boarded the ship in international waters, seized it at gunpoint and towed it to the city of Murmansk.