Carmakers are already fretting at the thought of achieving the new 35mpg CAFE standards imposed by the U.S. government, so imagine how they would feel if faced with a much stricter 44mpg being considered by California regulators. Officials are looking at raising restrictions over the next decade, culminating with a 44mpg standard by 2020 as proposed by the California Air Resources Board.

California is the single biggest market for cars in the world but what’s worse for carmakers is that a further 15 other states plan to adopt the new rules as well. Combined, these states account for more than half of the total U.S. market, so such a rule would almost certainly dictate the kinds of cars and trucks sold across the entire country, reports Automotive News.

As expected the industry is opposed to states setting their own greenhouse rules but major presidential candidates, John McCain, Hillary Clinton and Barack Obama are all in favor of the idea. If it were to come in, there would have to be a 62% improvement in fuel economy over today's vehicles. Another major hurdle would be convincing people to downgrade to much more fuel-efficient models, no easy task in car crazed California.