It's clear that there is a struggle going on between union leadership, that has been largely co-opted by the ruling class, and rank and file workers who support the Occupy movement. Ruling class political operatives are extremely concerned about the outcome of this contest and are putting a lot of effort into restraining union bosses from cooperating by engaging in a propaganda barrage in the media, and likely are putting other kinds of pressure on union bosses behind the scenes.
The potential of this new coalition--which was key to shutting down the Port of Oakland with a community picket of thousands on November 2--has clearly alarmed employers, who have launched an aggressive advertising campaign to denounce the December 12 effort. The Washington Post carried the same line, declaring that workers don't support the plan.Read also this piece by Danny Lucia from the same source entitled, "Co-opt-upy Wall Street?", for more details on co-opting union leadership.