More than 30 million vehicles in the United States could be affected by the defective air bags made by auto parts maker Takata Corp. and safety regulators in the U.S. should act quicker to replace the faulty parts, two prominent senators said.

"We believe that NHTSA should immediately issue a nationwide safety recall on all the affected cars, regardless of where the car is registered," Richard Blumenthal and Edward Markey said in a letter dated Thursday, referring to the National Highway Traffic Safety Administration.

Markey's office said that it used auto registration information and other data to calculate that more than 30 million vehicles could be equipped with defective air bags.