This document specifies Operations, Administration, and Maintenance (OAM) messages to indicate service disruptive conditions for MPLS-based transport network Label Switched Paths. The notification mechanism employs a generic method for a service disruptive condition to be communicated to a Maintenance Entity Group End Point. This document defines an MPLS OAM channel, along with messages to communicate various types of service disruptive conditions. [STANDARDS-TRACK]