March 11 (Reuters) - Toyota Motor Corp ( TM ) is recalling 550,007 vehicles in the U.S. as a faulty seat-back mechanism may fail to lock, increasing the risk of injury, the U.S. National Highway Traffic Safety Administration (NHTSA) said on Wednesday.

The recall includes certain 2021-2024 Highlander and Highlander Hybrid vehicles because the second-row seat backs may not lock into place during adjustment.

Dealers will replace the return springs in the seat-back recliner assemblies at no cost to owners, NHTSA said.