A U.S. safety regulator on Wednesday ordered Takata Corp. to preserve all air bag inflators removed through a recall process as evidence for a federal investigation and private litigation cases.

It was the first time the National Highway Traffic Safety Administration, an agency of the U.S. Department of Transportation, has ordered a company to preserve evidence for private litigation, said Gordon Trowbridge, a spokesman for NHTSA.

The defective parts, which activate air bags in case of collision — have been linked to at least six deaths and dozens of injuries, and have resulted in several lawsuits. NHTSA claims the air bags explode with too much force, spraying metal fragments at occupants.