Greenpeace says the environmental group's activists who were detained in Russia in September have been denied exit visas.
Twenty-six foreign nationals remain in Russia, free on bail but still awaiting trial on charges of hooliganism stemming from their protest at a Gazprom oil rig in the Barents Sea.
Greenpeace said it asked Russia to issue exit visas for the activists.
The request was refused and Greenpeace said its people "would now be forced to stay in St. Petersburg for Christmas and possibly well beyond."
Greenpeace spokeswoman Maria Favorskaya said the 26 could not receive exit visas because they did not have entry visas.
The entire crew of the Greenpeace vessel "Arctic Sunrise," which included four Russian nationals, was taken into custody and brought to Russia, where they originally faced charges of piracy.
Based on reporting by AFP and Reuters