This term was introduced into the Dutch language as "eco-fascisme" by legendary satiric duo Van Kooten en De Bie.
People that use violence to force their opinions upon others are generally called fascists. So called leftists that think its o.k. for them to wear skimasks and throw Molotov cocktails at government officials in the name of anti-globalization are called eco-fascists. The name is a pun on the practice of Dutch advertisers in the 1990's to put the additive 'eco' in front of product names to claim their environmental frienliness. Eco-gasoline, eco-nuclear power, eco-soap, etc.
In response to the below (and no, I didn't want this to turn into a discussion) I have two more remarks to add here.
First, the term fascism originated in Italy, where Mussolini had started fighting crews (called fasci di combattimento, hence the term fascism) to terrorize citizens into adopting his opinions. Fascism therefore is not defined as totalitarianism but as the practice of forcing one's opinion onto others through violence.
Smell the irony here! Van Kooten en De Bie invented this term to stress the awkward fact that self proclaimed leftist, anti-totalitarian groups seem to regard their own use of violence justified when it comes to their own causes, but strongly oppose it when portrayed by others. By no means did they set out to call leftists fascists. Just hypocrites maybe.