Graco argued that infant seats are used differently, and in an emergency, an adult can remove the whole seat rather than using the buckle.
When Graco announced the initial recall in February, NHTSA sent the company a sternly worded letter questioning why the infant seats weren't included. The agency said parents have filed complaints with the agency and the company about stuck buckles on the infant seats.
The letter also accused the company of soft-pedaling the recall with "incomplete and misleading" documents that will be seen by consumers. The agency threatened civil penalties.
But Graco, a division of Atlanta-based Newell Rubbermaid Inc., told The Associated Press at the time that rear-facing infant seats weren't being recalled because infants don't get food or drinks on their seats. Graco had agreed to send replacement buckles to owners of infant seats upon request.
In a June 27 letter to NHTSA, however, Graco said that further investigation showed a "higher than typical level of difficulty" in unlatching the infant seat buckles.
The company says there have been no injuries reported because of the problem. Spokeswoman Ashley Mowrey said in a statement that Tuesday's move, which brings the recall to 6.1 million seats, comes after months of sharing data and research with NHTSA. The company said the recall "is in the best interest of consumers and underscores our shared commitment to child passenger safety."
Infant-seat models covered by Tuesday's recall include the SnugRide, SnugRide Classic Connect (including Classic Connect 30 and 35), SnugRide 30, SnugRide 35, SnugRide Click Connect 40, and Aprica A30. They were manufactured between July 2010 and May 2013, according to NHTSA.
Graco will replace the buckles for free. The company says owners can check to see if their seats are included by going to www.GracoBuckleRecall.com or by calling (877) 766-7470.