WASHINGTON, D.C. --- Transportation Secretary Mary E. Peters on Tuesday, April 22, unveiled new proposed federal fuel-economy standards that would require cars and trucks to get an average of 31.6 miles per gallon by 2015 -- a major increase over the current fleet.

However, the plan -- outlined in a 417-page document issued by the National Highway Traffic Safety Administration -- includes language that bars California and other states from regulating automobile greenhouse gas emissions, the Los Angeles Times reported. The proposed rules will be open for a 60-day comment period, after which a final version will go into effect.

California Attorney General Jerry Brown said the state will ask for the language at issue, which starts on page 374, to be removed. "We think this is illegal under federal laws," Brown said.

The NHTSA, however, said it rejected the notion that states have the right to set their own greenhouse gas standards separate from federal mileage standards.

The new proposal requires that cars reach an average efficiency of 35.7 mpg by 2015 and light trucks must reach 28.6 mpg. Under legislation passed in 2007, the overall average must reach 35 mpg by 2020.