It's hard to believe, but there are two writeups in this node that define organizations with names taking the form of "E* Liberation Front," but no one's mentioned the Earth Liberation Front....
The E.L.F. is a group of... well, what they get called depends largely on the referrer's opinions of E.L.F. They have been called terrorists, in particular by the F.B.I., although they have yet to kill a single human being. The term "saboteurs" is perhaps more accurate. E.L.F. engages in acts of "ecotage," or in their own words "economic sabotage." They destroy bulldozers, demolish buildings and erect blockades. Localized arson is commonly used. Spiking trees is not enough for them. However, professing respect for all life, they are as reluctant to harm human beings (at least, in a physical sense) as they are to squash squirrels or truncate trees.
Their structure is decentralized. They claim not to have leaders or infrastructure. They encourage small, scattered groups to commit acts under their banner, but they do not coordinate them. They have a public spokesman for the purposes of releasing information, who agrees with their aims but does not possess knowledge of who does what.
The E.L.F.'s aims and some of its membership coincides with the A.L.F., the "Animal Liberation Front." E.L.F. arose out of Earth First!, when that organization began to eschew illegal means.
How unavoidable it is in this modern age that even groups whose stated intent is the breaking of laws and the destruction of property have a website! Theirs is:
http://www.earthliberationfront.com/main.shtml
Their FAQ, in PDF format (difficult to read on-line), is at:
http://www.earthliberationfront.com/library/elf_faq.pdf
Sources:
http://www.earthliberationfront.com/about/
http://www.abcnews.go.com/sections/science/DailyNews/protest990120.html
http://www.furcommission.com/debate/words6.htm