WASHINGTON (AP) — The National Highway Traffic Safety Administration says it is investigating whether Graco took too long to report a safety defect in its child car seats.

Graco Children’s Products Inc., a division of Atlanta-based Newell Rubbermaid Inc., recalled more than six million car seats this year because their buckles could get stuck. That could put a child’s life at risk in an emergency. It is the largest child seat recall in U.S. history.

Federal rules require a manufacturer to report a safety defect within five days of becoming aware of it. If the investigation finds the company failed to report the defect in a timely manner, the company could face up to $35 million in fines.

A Graco representative could not be reached immediately for comment Monday.