A Texas-based company claims the environmental advocacy group tried to delay construction of the Dakota Access Pipeline with protests.

Greenpeace USA headed to court in North Dakota on Monday, as a trial expected to last about five weeks begins over protests at the construction site of Energy Transfer's (NYSE:ET) Dakota Access Pipeline that delayed the $3.

The trial in North Dakota that observers are describing as a key free speech rights case has begun. Energy Transfer, a Texas-based company and the operator of the Dakota Access Pipeline, is suing Greenpeace for alleged defamation and what their lawyers describe as a “campaign of violence.”