Beginning in January The state of California will no longer purchase fleet vehicles from automakers that do not sign on to a voluntary agreement to improve fuel economy. This is a substantial toughening of the state's position on regulating greenhouse gas emissions. It also goes around the EPA's authority as the state can make purchasing decisions based in any criteria they wish.
GM will be hit particular hard as they will lose tens of millions of dollars worth of sales annually.
Currently Honda, Volkswagen, Ford, and BMW are the only signatories to the deal while other automakers have opposed California's authority to regulate greenhouse gasses in court.
The state will also no longer purchase gasoline-powered sedans effective immediately (excluding public safety vehicles). It is unclear if this will allow TZEV (i.e. plug-in hybrids) to serve the state's most rural areas or if it is limited to battery and fuel-cell electric vehicles.