A horizontal adjustment mechanism for use with a chair having a base, a seat supported on the base and a seat back. The mechanism includes a first plate that is to be coupled to the base and a second plate that is coupled to the seat. The second plate includes a mating portion. The second plate is slidably coupled to the first plate such that the second plate can move relative to the first plate. The mechanism also includes a lever mechanism. The lever mechanism includes a mating portion that selectively disengages from the mating portion of the second plate to allow the second plate to move relative to the first plate.