This article reports:
In addition to the fact that the young men are required to perform service despite the exceptions in the law, or that their family depends on their salary or conscientious objection, they are held incommunicado without being able to tell their relatives for several days.
The Colombian Constitutional Court ruled in 2011 that the raids were clearly illegal. In addition, the Working Group on Arbitrary Detention of the UN Human Rights Committee ruled that Colombia had violated Articles 9 and 18 of the International Covenant on Civil and Political Rights. [Rough Google translation.]