If deep ecologists represent the ideological extreme of the Greens, organizations such as the Earth Liberation Front (ELF) and Animal Liberation Front (ALF) represent the political extremes. Characterized as eco-terrorists by some governments, these groups resort to crimes such as sabotage, vandalism, and arson in their efforts to protect the environment or animals. According to some of these activists, violence against nature justifies violence to protect it. These groups are generally leaderless and without hierarchical structure. Adherents act independently or through locally comprised groups. They may share ideology and tactics but do not generally have rigid group structures.
Tree spiking was a common tactic of ELF activists. This involved pounding metal spikes into trees that when cut with chainsaws would damage the equipment and potentially cause physical injury to those doing the cutting. ALF activists, who are concerned with animal cruelty and animal rights issues, damaged, often through arson, buildings associated with the use of animals for food (butcher shops, restaurants, and animal farms), clothing (primarily fur-oriented businesses), research, or entertainment. These groups are at the fringes of the Green movement. They were most active in the 1970s and 1980s and have been less active since.