The environmental group is being sued for $300 million in North Dakota by a pipeline company in a case that has become a flash point in the debate over free speech.

A US oil pipeline operator's lawsuit seeking millions of dollars from Greenpeace for allegedly orchestrating a campaign of violence and defamation begins Monday in a North Dakota court, in a case with broad free speech implications.

Energy Transfer says Greenpeace used tactics including defamation, vandalism and harassment in an attempt to tarnish the company’s reputation and sink the Dakota Access Pipeline project.