A firm’s ability to raise its prices is usually constrained by competitors and the possibility that its customers can switch to alternative sources of supply. When these constraints are weak, a firm is said to have market power and if the market power is great enough, to be in a position of dominance or monopoly (the precise terminology differs according to the jurisdiction).
While mere possession of monopoly power does not in itself constitute violation of competition laws, the abuse of such power particularly if it is used to weaken competition further by excluding rivals, calls for intervention from competing authorities.