Graco Children’s Products added more than 403,000 child car seats to its February 2014 recall of 3.8 million, to replace faulty harness buckles, and the National Highway Traffic Safety Administration (NHTSA) wants Graco to add another 1.8 million infant seats with the same buckles to the recall.

Buckles can get gummed up by food and drinks, making it difficult to remove children in an emergency. NHTSA says it has received at least 80 complaints about the seats from parents who say they have had to use excessive force to unlatch the harness buckle. In some cases, the straps had to be cut to free children.

The 403,222 child seats recalled include 2006 through 2014 Argos 70 Elite, Ready Ride, Step 2, My Ride 65 with Safety Surround, My Size 70, Head Wise 70 with Safety Surround, Nautilus 3-in-1, Nautilus Plus, and Smart Seat with Safety Surround. The recall, now at 4.2 million, is the fourth-largest child seat recall in American history. If the SnugRide infant seats are added, it would be the largest such recall.

Although Graco has admitted that “food and dried liquids can make some harness buckles progressively more difficult to open over time or become stuck in the latched position,” it has refused to recall seven infant seat models with the faulty buckles, according to a National Highway Traffic Safety Administration recall notice. The agency and company continue to negotiate on whether a recall is warranted for the SnugRide infant seats, and NHTSA has threatened civil penalties and told the company to remove statements from public documents that underplay the seriousness.

A study released Feb. 4, 2014 by the U.S. Centers for Disease Control and Prevention (CDC) reports more than 9,000 car accident deaths among children 12 and younger from 2002 to 2011.