For those looking for more information than I can stomach on the subject go to the always on top of things Finke.

FOR THE TL;DR CROWD:
SAG contracts are up with the AMPTP (studios/producers/media companies). AMPTP wants them to use the same formula as the deal they made with the Writers. SAG eventually agreed, but want to make over 70 changes (including wage hikes up to 200%). This would lead to enormous cost increases. Studio's will likely not green-light any new projects because of fear of the strike, which could last to mid-July.