Co-existence mechanisms for shared spectrum and unlicensed spectrum are disclosed. Several base stations, from one or more network operators, share a communication spectrum in a base non-contention procedure state. When a given base station determines that communications with its served user equipments (UEs) suffers a diminished quality, the base station transmits a diminished quality indicator in response. Subsequent communications with the served UEs over the shared spectrum would then occur using a contention-based procedure state triggered by the diminished quality indicator. The triggering of the contention-based procedure may be made by the base station on either sending the diminished quality indicator or receiving a similar indicator from a neighbor base station, or by an indication from a central controller making a determination to initiate contention-based procedures based on flags received from the neighboring base stations.