Here are articles by Meredith Aby and Mike Kelly writing about Columbian Unions on a pro-FARC and Socialist website. So, it does look like they were very sympathetic to a terrorist group.
Summer 2004 Colombia's Unions: Under Attack and Fighting Back by Meredith Aby
Summer 2004 Coca-Cola Attempts Union Busting in Colombia by Meredith Aby
Freedom Road Socialist Organization