A method and apparatus for triggering of transmission carrier or resource reselection in a wireless communication system is provided. A first wireless device reserves a set of resources comprising at least a first resource and a second resource for sidelink transmission. When (i) the sidelink transmission using the first resource overlaps with an uplink transmission, and (ii) a priority of the uplink transmission is higher than a threshold, the first wireless device clears the first resource from the set of resources, and adds a third resource to the set of resources.