Although, to be fair, requirements is a stronger word than what I should use. Although there are fines to automakers who fail to meet these rules, the fines themselves are quite small. It's the bad publicity for failing to meet the guidelines that Toyota, Honda, et al are more worried about.
Green Car Congress has the story from the Nikkei on the new requirements on average fuel economy for the carmakers in Japan. By 2015, passenger cars need to have an average fuel economy of 39.5 mpg (see the table below).
|Proposed Average Fuel Economy|
|Vehicle class||2004 value||2015 est. value||% change|
|Source: Ministry of Economy, Trade and Industry.|
|Passenger cars||13.6 km/liter |
32.0 mpg US
|16.8 km/liter |
39.5 mpg US
|Small buses||8.3 km/liter |
19.5 mpg US
|8.9 km/liter |
21.0 mpg US
|Light cargo trucks||13.5 km/liter |
31.8 mpg US
|15.2 km/liter |
35.8 mpg US
Compare that to the US Corporate Average Fuel Economy (CAFE) standards. In 2006, the fleet requirement for passenger cars was 27.5 mpg and 20.7 mpg for light trucks. (If you're interested in seeing who's paid fines for not meeting these requirements, as well as how much, the NHTSA has a table of fines.
CAFE standards have been changed to look at a vehicles "footprint" — the product of its wheelbase and track. Some critics point out that this may have the unintended consequence of pushing manufacturers to make ever-larger vehicles to avoid strict economy standards.