Writers Guild of America Strike
From Super-wiki
On November 5, 2007, writers for film and TV Shows, including “Supernatural”, began a strike after the breakdown of negotiations between the union and the association representing more than 350 production companies and studios which employ them.
The main issues in dispute concerned payment (“residuals”) to writers arising from the distribution of film and TV in new media areas including DVD and the Internet. Playbill
As the strike began Supernatural has 10-12 episodes completed; roughly five scripts that are ready to shoot. La Times