(CNN) -- Federal regulators are asking Graco Children's Products why it is not including infant seats in a major recall of child car seats.
The company last month voluntarily recalled 3.7 million child car seats after regulators said the red release button in the harness can become stuck, preventing quick removal of a child in an emergency.
But Graco Children's Products declined to recall an additional 1.77 million infant seats with the same problem, according to the government.
On its web site, the company said it did not recall the rear-facing infant seats because there is a second way to release them.
"They are uniquely designed to detach from their base for quick release if needed," the company said.
On Thursday, the National Highway Traffic Safety Administration demanded more information.
NHTSA asked the company to explain its "reasoning and rationale" for excluding the infant seats from the recall.
On Friday, Graco said it would comply with the request for information.
"Our car seats comply with all NHTSA's stringent performance standards and have withstood rigorous testing that far exceeds federal requirements," the company said in a statement. "Despite this, for any concerned parent or guardian, we will continue to offer a replacement harness buckle at no cost."
Graco's recall included 3.7 million seats across 11 models manufactured between 2009 and 2013.
The models involved: Cozy Cline, Comfort Sport, Classic Ride 50, My Ride 65, My Ride with Safety Surround, My Ride 70, Size 4 Me 70, Smartseat, Nautilus, Nautilus Elite, and Argos 70.
But it declined the request to recall seven models that include rear-facing seats: Snugride, Snugride 30, Snugride 32, Infant Safe Seat-Step 1, Snugride 35, Tuetonia 35, and Snugride Click Connect 40.