At the heart of the case is the Dakota Access Pipeline, where nearly a decade ago the Standing Rock Sioux tribe led one of the largest anti-fossil fuel protests in US history. Hundreds were arrested and injured, prompting concerns from the United Nations over violations of Indigenous sovereignty.

The pipeline, which transports fracked crude oil to refineries and global markets, has been operational since 2017.

But its operator, Energy Transfer, has continued pursuing legal action against Greenpeace -- first in a federal lawsuit seeking $300 million, which was dismissed, and then in the three-week trial in a state court in Mandan, North Dakota.

Critics call the case a clear example of a Strategic Lawsuit Against Public Participation (SLAPP), designed to silence dissent and drain financial resources. Notably, North Dakota is among the minority of US states without anti-SLAPP protections.

In February, Greenpeace became the first group to test the European Union's anti-SLAPP directive by suing Energy Transfer in the Netherlands. The group is seeking damages with interest and demanding that Energy Transfer publish the court's findings on its website.

More than 400 organizations, along with public figures such as singer Billie Eilish and actors Jane Fonda and Susan Sarandon have signed an open letter in support of Greenpeace, as have hundreds of thousands of individuals globally.