Supermarket chains that are suffering worker strikes in five states say that in order to compete with Wal-Mart they must keep their labor costs down. In recent years, Wal-Mart has edged into the grocery business with its Supercenter stores. Officials with Kroger and other chains say that because Wal-Mart does not have to pay the same union labor costs, it can pass lower prices onto the customer. Kroger officials say that in West Virginia -- one of the states where workers are striking -- they have to pay about six dollars an hour more per worker than Wal-Mart. It can run as fourteen dollars more in other states. Wal-Mart, which is based in Bentonville, says its lower prices are mainly due to its efficient distribution system and large buying power.