 Amnesty International reported in 2007 that for cases in which the perpetrator was known, paramilitaries were responsible for 49% of the attacks against trade-unionists, state forces were responsible for 43%, and the guerrilla forces were responsible for 2%.According to the National Labour School (ENS), a Colombian NGO monitoring trade union violence, impunity for crimes committed against trade unionists is running at 94%.Trade union membership in Colombia has fallen dramatically since the 1980s.