TOKYO (Reuters) - Shares of Takata Corp (>> Takata Corporation) fell as much as 6.8 percent on Thursday morning after U.S. auto safety regulators ordered it to expand its regional recall of driver-side air bags to cover the entire United States.

Such a nationwide recall would affect vehicles made by five automakers: Ford Motor Co (>> Ford Motor Company); Honda Motor Co (>> Honda Motor Co Ltd); Chrysler Group LLC, a unit of Fiat Chrysler Automobiles  (>> FIAT SPA); Mazda Motor Corp (>> Mazda Motor Corp) and BMW AG (>> Bayerische Motoren Werke AG).

The National Highway Traffic Safety Administration gave Takata until Tuesday to issue a recall. If the company does not, NHTSA "may begin proceedings" leading to fines for the Japanese air bag supplier of up to $7,000 per vehicle that the U.S. road safety regulator says should have been recalled.

Takata has resisted expanding the recall beyond the initial regional "high humidity" areas.

(Reporting by Chang-Ran Kim; Editing by Chris Gallagher)