All U.S. translator and booster stations are low-power and have a class D license, making them secondary to other stations (including the parent); they must accept interference from full-power (100 watts or more on FM) stations, while not causing any of their own. Boosters must not interfere with the parent station in the community of license. Licenses are automatically renewed with that of the parent station and do not require separate applications, although the renewal may be challenged with a petition to deny. FM booster stations are given the full call sign (including an -FM suffix, even if there is none assigned) of the parent station plus a serial number such as WXYZ-FM1, WXYZ-FM2, etc.