In an interview given on August 20, 2003, the vice-president answers your question by saying that there are many enemies of unionization. Union leaders are mainly the victims of the paramilitary, but there is also the FARC and the national liberation army. There are also business people and company presidents who do not want to see their workers organized under unions and who give out contracts to have these people eliminated.
It is the vice-president himself who gave that response.