WASHINGTON (CNN) -- Federal officials on Wednesday recalled up to 55,000 Fisher-Price children's car seats, because of a possible malfunction in the mechanism that locks the shoulder harness.

Until free modification kits arrive, parents can continue to use the seats, as long as they check them each time to be sure the harness belts are locked in place.

The recall involves Model Number 79700 Safe Embrace convertible car seats, which are used in a rear-facing position for infants weighing up to 22 pounds and in a forward-facing position for toddlers weighing up to 40 pounds.

The seats were manufactured from May 19, 1997, through March 29, 1998.

Fisher-Price learned through its consumer research that the current harness adjuster, which is used to tighten and lock the harness belts around a child, may malfunction if a spring breaks or dislocates from the correct position.

When the mechanism fails, it may not properly lock the shoulder belts in place. If this occurs, the child would not be adequately protected in a crash, the National Highway Traffic Safety Administration said.

Neither Fisher-Price nor NHTSA has had any reports of injuries as a result of the problem.

People who have the Safe Embrace convertible car seat should contact Fisher-Price at 1-800-355-8882 between 8 a.m. and 6 p.m. EDT Monday through Friday to obtain a replacement harness adjuster.

Car-seat owners also may write Fisher-Price Consumer Affairs at the following address: 636 Girard Avenue, East Aurora, New York 14052.

Those who have registered their convertible car seats with the company will automatically receive the kits.