EPA (Enable Polluters Agency) tries to Change Fuel Efficiency Standards to allow More Pollution, More Profits for Corporations.

http://time.com/5347862/epa-andrew-wheeler-fuel-efficiency-california/

Opposing California, New EPA Head Calls for Single U.S. Fuel Efficiency Standard. 

In General, California has stricter standards and car makers comply to California Requirements instead of designing two different styles of cars, one for California and One for the other states.