U.S. auto safety regulators say they stand by a conclusion that more than 50 million air bag inflators are dangerous and should not be in use, taking another step toward a massive recall.

The decision Wednesday by the National Highway Traffic Safety Administration involves inflators made by ARC Automotive Inc. in Tennessee and another parts manufacturer. It comes despite opposition from automakers.

The inflators in about 49 million vehicles from 13 manufacturers can explode and hurl shrapnel into drivers and passengers.

The agency has said the inflators are responsible for at least seven injuries and two deaths in the United States and Canada since 2009.