The environmental activist group Sea Shepherd is asking Germany's government to block the extradition of its founder Paul Watson.
The 61-year-old Canadian was detained at Frankfurt Airport on Sunday on an arrest warrant from Costa Rica.
The Central American country claims he endangered a fishing boat and its crew in 2002.
Sea Shepherd's ship operations officer Peter Hammarstedt said Tuesday that the group wants the German Justice Ministry to declare Costa Rica's request invalid.
Under German law, the government can intervene at all stages of the three-month extradition process.
Sea Shepherd said Watson was filming a documentary in 2002 when his team encountered an illegal shark-finning operation in Guatemalan waters.
The U.S.-based group has a history of waging aggressive campaigns to protect whales, dolphins and other marine animals.