WASHINGTON, D.C. — The National Highway Traffic Safety Administration (NHTSA) has opened an investigation into the timeliness of Graco Children’s Products Inc.’s reporting of a safety defect in child seats.

The defect involves buckles of child and infant car seats that stick or become stuck in the latched position, which NHTSA said creates “an unreasonable risk to a child’s life in the event of an emergency.”

After continued pressure from NHTSA, Graco eventually recalled more than 6 million defective car seats earlier this year — the largest child seat recall in U.S. history.

“The Department [of Transportation] is committed to ensuring that parents have peace of mind knowing that the car seat in which they are placing their child and their trust is safe and reliable,” U.S. Transportation Secretary Anthony Foxx said. “Any delays by a manufacturer in meeting their obligations to report safety issues with the urgency they deserve, especially those that impact the well-being of our children, erodes that trust and is absolutely unacceptable.”

Under the National Traffic and Motor Vehicle Safety Act, once a manufacturer knows or should reasonably know that an item of motor vehicle equipment, such as a car seat, contains a safety-related defect, the manufacturer has a maximum of five business days to notify the agency. NHTSA officials said that the agency’s investigation will evaluate the facts of the case to determine whether Graco violated the law.

“There is no excuse for delaying a recall to address any safety-related defect,” NHTSA Deputy Administrator David Friedman said. “If Graco delayed in protecting children and infants from this defect, we will hold them accountable.”

If NHTSA’s investigation finds that Graco was untimely in reporting the defect, the manufacturer could be fined up to $35 million in civil penalties. The administration’s four-year reauthorization bill — the GROW AMERICA Act — proposes to increase the congressionally established cap on fines from $35 million to $300 million. The Department of Transportation transmitted the GROW AMERICA Act to Congress in spring 2014.